LIBRARY 

OF    THE 

UNIVERSITY  OF  CALIFORNIA. 
Class 


EARTH    DAMS 


A    STUDY 


BY 


BURR  BASSELL,    M.  Am.  Soc.  C.  E. 
n 

Consulting'   Engineer 


NEW  YORK 

THE   ENGINEERING    NEWS  PUBLISHING   COMPANY 
1904 


COPYBIGHT,   1904 
BY 

THE  ENGINEERING  NEWS  PUBLISHING  Co. 


ACKNOWLEDGMENTS. 


The  writer  wishes  to  acknowledge  his  appreciation  of  the  assist- 
ance given  him  by  Mr.  Jas.  D.  Schuyler,  M.  Am.  Soc.  C.  E.,  Con- 
sulting Hydraulic  Engineer,  in  reviewing  this  paper,  and  in  making 
suggestions  of  value.  Appendix  II.  contains  a  list  of  authors 
whose  writings  have  been  freely  consulted,  and  to  whom  the 
writer  is  indebted ;  the  numerous  citations  in  the  body  of  the  paper 
further  indicate  the  obligations  of  the  writer. 


CONTENTS. 


CHAPTER  I. 

PAGE 
Introductory    I 


CHAPTER  II. 
Preliminary  Studies  and  Investigations 


CHAPTER  III. 
Outline  Study  of  Soils.     Puddle 12 

» 

CHAPTER   IV. 

The   Tabeaud   Dam,    California • 17 

CHAPTER  V. 
Different   Types   of   Earth    Dams 33 

CHAPTER  VI. 
Conclusions    • 63 

APPENDIX  I. 
Statistical  Descriptions  of  High  Earth  Dams 67 

APPENDIX  II. 
Works  of  Reference...  ..68 


ILLUSTRATIONS. 


PAGE 
Fig.     I.     Longitudinal  Section  of  Yarrow  Dam  Site 10 

2.  Cross-Section  of  the  Yarrow  Dam 10 

3.  Plan  of  the  Tabeaud  Reservoir 17 

4.  Tabeaud  Dam:  Plan  Showing  Bed  Rock  Drains ..18 

5.  Details    of    Drains . '. 18 

6.  View   of   Drains 19 

7.  North  Trench    20 

8.  South   Trench    '. 21 

9.  Main    Central    Drain 21 

10.  Embankment   Work    23 

11.  Dimension   Section    26 

12.  Cross  and  Longitudinal  Sections 27 

13.  View  of  Dam  Immediately  After  Completion 29 

14.  Cross-Section    of    Pilarcitos    Dam 34 

15.  San   Andres    Dam 34 

16.  Ashti    Tank    Embankment 35 

17.  Typical  New  England  Dam 40 

18.  Two  Croton  Valley  Dams  Showing  Saturation 41 

19.  Studies  of  Board  of  Experts  on  the  Original  Earth  Portion  of 

the  -New  Croton  Darn 43 

20.  Studies  of  Jerome  Park  Reservoir  Embankment 46 

21   to  24.     Experimental   Dikes  and  Cylinder  Employed  in   Studies 

for  the  North  Dike  of  the  Wachusett  Reservoir 49 

25.  Cross-Section  of  Dike  of  Wachusett  Reservoir 49 

26.  Working  Cross-Section  of  Druid  Lake  Dam 53 

27  to  29.     Designs  for  the  Bohio  Dam,  Panama  Canal •  -55 

30.  Cross-Section  of  the  Upper  Pecos  River  Rock- Fill  Dam 59 

31.  Developed  Section  of  the  San  Leandro  Dam 59 


VI 


EARTH     DAMS 


CHAPTER   I. 

Introductory. 

The  earth  dam  is  probably  the  oldest  type  of  dam  in  existence, 
antedating  the  Christian  Era  many  hundreds  of  years.  The  litera- 
ture upon  this  subject  is  voluminous,  but  much  of  it  is  inaccessible 
and  far  from  satisfactory.  No  attempt  will  here  be  made  to  collate 
this  literature  or  to  give  a  history  of  the  construction  of  earth  dams, 
however  interesting  such  an  account  might  be.  The  object  will 
rather  be  to  present  such  a  study  as  will  make  clear  the  application 
of  the  principles  underlying  the  proper  design  and  erection  of  this 
class  of  structures.  In  no  way,  therefore,  will  it  assume  the 
character  or  dignity  of  a  technical  treatise. 

Dams  forming  storage  reservoirs,  which  are  intended  to  impound 
large  volumes  of  water,  must  necessarily  be  built  of  considerable 
height,  except  in  a  very  few  instances  where  favorable  sites  may 
exist.  Recent  discussions  would  indicate  that  a  new  interest  has 
been  awakened  in  the  construction  of  high  earth  dams.  As  related 
to  the  general  subject  of  storage,  it  is  with  the  high  structure  rather 
than  the  low  that  this  study  has  to  do.  To  the  extent  that  "the 
greater  includes  the  less,"  the  principles  here  presented  are  ap- 
plicable to  works  of  minor  importance. 

Many  persons  who  should  know  better  place  little  importance 
upon  the  skill  required  for  the  construction  of  earthwork  embank- 
ments, considering  the  work  to  involve  no  scientific  problems.  It 
is  far  too  common  belief  that  any  ordinary  laborer,  who  may  be  able 
to  use  skillfully  a  scraper  on  a  country  road,  is  fitted  to  superintend 
the  construction  of  an  earth  dam.  It  has  been  said  that  the  art  of 
constructing  earth  dams  is  purely  empirical,  that  exact  science  fur- 
nishes no  approved  method  of  determining  their  internal  stresses, 
and  that  in  regard  to  their  design  experience  is  much  more  valua- 
ble than  theory.  When  the  question  of  stability  is  fully  taken  into 
consideration,  it  certainly  requires  a  large  amount  of  skill  success- 
fully to  carry  out  works  of  this  character. 

Extreme  care  in  the  selection  of  the  site,  sound  judgment  in  the 
choice  of  materials  and  assiduity  in  superintending  the  work  while 
in  progress,  are  all  vitally  essential. 


2  EARTH  DAMS. 

Classification   of   Dams. 

Dams  may  be  classified  according  to  their  purpose  as  diverting 
dams  or  weirs  and  as  storage  dams.  The  former  may  be  located 
upon  any  portion  of  a  stream  where  the  conditions  are  favorable, 
and  the  water  used  for  manifold  purposes,  being  conveyed  by  means 
of  canals,  flumes,  tunnels  and  pipe  lines  to  places  of  intended  use. 
These  dams  are  generally  low  and  may  be  either  of  a  temporary 
01  permanent  character,  depending  upon  the  uses  to  which  the  wa- 
ter is  put.  Temporary  dams  are  made  of  brush,  logs,  sand  bags, 
gravel  and  loose  rock.  The  more  permanent  structures  are  built  of 
stone  and  concrete  masonry. 

Storage  dams  may  be  classified  according  to  the  kind  of  material 
entering  into  their  structure,  as  follows:  (i)  Earth;  (2)  Earth  and 
Timber;  (3)  Earth  and  Rock-fill;  (4)  Rock-fill;  (5)  Masonry;  (6) 
Composite  Structures. 

Low  dams  forming  service  reservoirs  for  domestic  water  sup- 
plies and  for  irrigation  comprise  by  far  the  most  numerous  class. 
They  are  not  designed  to  impound  a  large  volume  of  water  and 
therefore  may  be  built  across  a  small  ravine  or  depression,  or  even 
upon  the  summit  of  a  hill,  by  excavating  the  reservoir-basin  and 
using  the  material  excavated  to  form  the  embankment.  These  res- 
ervoirs may  be  used  in  connection  with  surface  or  gravity  systems, 
artesian  wells,  or  underground  supplies  obtained  by  pumping.  The 
dams  forming  these  reservoirs  being  of  moderate  size  and  height 
may  vary  greatly  in  shape  and  dimensions.  The  form  may  be  made 
to  suit  the  configuration  of  the  dam  site.  When  the  earthwork  re- 
quires it,  they  may  be  lined  with  various  materials  to  secure  water- 
tightness.  Often  such  dams  are  made  composite  in  character, 
partly  of  earth  and  partly  of  masonry  or  some  other  material.  They 
are  also  frequently  accompanied  by  numerous  accessories,  such  as 
settling-basins,  aerating  devices  and  covers,  which  present  a  diver- 
sity in  form  and  appearance.  A  presentation  of  the  different  types 
of  dams  thus  employed,  with  a  discussion  of  the  questions  pertain- 
ing to  utility  in  design  and  economy  in  construction,  would  be  ex- 
ceedingly valuable  and  of  general  interest.  Service-reservoirs  will 
receive  only  a  passing  notice,  with  the  hope  expressed  that  some 
competent  authority  will  discuss  them  in  the  future. 


CHAPTER  II. 
Preliminary  Studies  and  Investigations. 

The  preliminary  studies  and  investigations  which  should  be  made 
prior  to  the  construction  of  any  dam  for  the  storage  of  water  have 
to  do  with  (i)  the  Catchment  Area,  (2)  the  Reservoir  basin,  and  (3) 
the  Dam  site. 

Catchment   Area. 

It  is  thought  desirable  to  define  a  number  of  terms  as  we  proceed, 
for  the  purpose  of  correcting  erroneous  usage  and  for  a  clearer 
understanding  of  the  subject.  The  catchment  area  of  a  reservoir 
is  that  portion  of  the  country  naturally  draining  into  it.  The  water- 
shed is  the  boundary  of  the  catchment  area  and  may  be  correctlv 
defined  as  the  divide  between  adjacent  drainage  systems.  In  re- 
gard to  the  catchment  area  it  is  necessary  to  determine : 

1.  Its  extent  and  area  in  square  miles. 

2.  Its  topography  or  the  character  of  its  surface. 

3.  Its  hydrography  or  precipitation  and  run-off. 

4.  Its  geology,  or  the  character  of  its  soils  and  subsoils,  and  the 

nature  and  dip  of  its  rock  strata. 

5.  Its  flora,  or  the  extent  to  which  it  is  clothed  with  forest  trees 

or  other  vegetation. 

All  of  these  elements  affect  the  volumes  of  maximum  run-off, 
which  is  the  one  important  factor  in  the  construction  of  earth  dams 
that  must  not  be  underestimated. 

If  the  proposed  dam  or  reservoir  is  to  be  located  upon  a  main 
drainage  line;  that  is,  upon  a  river  or  stream,  it  is  necessary  to 
know  both  the  flood  and  low-water  discharge  of  the  stream.  Fre- 
quently no  reliable  data  on  this  subject  are  available,  and  the  engi- 
neer must  then  make  such  a  study  of  the  whole  situation  as  will  en- 
able hirq  to  estimate  the  minimum  and  maximum  flow  with  con- 
siderable accuracy. 

There  are  numerous  factors  entering  into  the  solution  of  this  first 
problem,  such  as  the  shape  and  length  of  the  catchment  area,  its 
general  elevation,  the  character  of  its  surface,  whether  mountainous, 
hilly  or  flat,  barren  or  timbered. 

Good  topographic  maps,  if  available,  furnish  valuable  data  on 


4  EARTH  DAMS. 

these  subjects  and  it  is  to  be  regretted  that  only  a  comparatively 
small  portion  of  the  United  States  has  been  thus  mapped  in  detail. 

The  results  of  stream  measurements,  if  "any  have  been  made  in 
the  catchment  basin,  are  especially  important :  These  are  usually 
few  in  the  high  areas,  on  account  of  their  inaccessibility.  The  year 
1902  marked  a  notable  beginning  of  such  measurements  in  Califor- 
nia. In  many  parts  of  the  arid  region  of  the  United  States,  the 
best  storage-sites  are  situated  in  the  upper  or  higher  portions  of 
the  drainage  systems.  This  is  especially  true  of  the  streams  on  the 
Pacific  Slope  having  their  source  in  the  High  Sierras.  As  regulators 
of  stream-flow  and  for  power  purposes  such  storage  is  peculiarly 
valuable,  while  storage  for  irrigation  and  domestic  uses  may  be  lo- 
cated nearer  the  valleys  and  the  centers  of  population. 

Frequently  the  engineer  is  required  to  build  his  dam  where  no 
such  data  are  available.  In  such  instances  he  should  endeavor  to 
secure  the  establishment  of  rain  gages  and  make  measurements  of 
the  flow  of  the  main  stream  and  its  principal  tributaries  at  various 
places  to  obtain  the  desired  information.  Even  this  may  not  suffice, 
owing  to  the  limited  time  at  his  disposal,  and  he  must  resort  to  the 
use  of  certain  empirical  rules  or  formulas,  and  make  such  compari- 
sons and  deductions  from  known  conditions  and  results  as  will  best 
answer  his  purpose. 

The  engineer  should  know,  approximately  at  least,  the  normal 
yield  of  the  catchment  area,  the  duration  of  the  minimum  and  max- 
imum seasonal  flow,  and  the  floods  he  may  have  to  provide  against 
during  the  construction  of  his 'dam.  These  data  are  absolutely  nec- 
essary to  enable  him  to  provide  ample  wasteways  for  his  reservoirs. 
Many  of  the  failures  of  earth  dams  have  been  the  result  of  over- 
topping the  embankment,  which  would  have  been  averted  by  an 
ample  wasteway.  The  most  notable  example  of  this  kind  in  recent 
years  was  that  of  the  South  Fork  Dam,  at  Conemaugh,  Pennsyl- 
vania, in  1889,  resulting  in  what  is  generally  known  as  the  "Johns- 
town Disaster." 

There  are  several  empirical  rules  and  formulas  for  calculating 
the  run  off  from  catchment  areas  and  for  determining  the  size  of 
spillways  necessary  to  discharge  this  flow  with  safety  to  the  dam. 
The  proper  formula  to  apply  in  any  given  case,  with  the  varying 
coefficients  of  each,  involves  a  thorough  knowledge  on  the  part  of 
the  designing  engineer  of  the  principles  upon  which  the  different 
factors  are  based. 

It  is  unwise  and  often  hazardous  to  make  use  of  any  important 


PRELIMINARY  STUDIES  AND  INVESTIGATIONS.  5 

hydraulic  formula  without  knowing  the  history  of  its  derivation. 
Experiments  are  not  always  properly  conducted,  and  often  the  de- 
ductions therefrom  are  unreliable.  A  presentation  and  discussion 
of  these  formulas  would  require  more  space  than  can  be  given  in 
this  study,  and  the  technical  reader  must  therefore  consult  for  him- 
self, as  occasion  may  require,  the  various  authorities  cited.  Form- 
ulas for  the  discharge  or  run-off  from  catchment  areas,  as  deter- 
mined by  Messrs.  Craig,  Dickens,  Ryves  and  others,  are  given  by 
most  writers  on  the  subject  of  hydraulics. 

Reservoir   Basin. 

The  next  subject  of  inquiry  relates  to  the  reservoir  basin.  It  is 
necessary  that  its  area  and  capacity  at  different  depths  should  be 
definitely  known,  and  this  information  can  only  be  obtained  by  hav- 
ing the  basin  surveyed  and  contoured.  A  map  should  be  made 
showing  contours  at  intervals  of  2  to  10  ft.,  depending  upon  the 
size  of  the  basin  and  the  use  to  which  the  reservoir  is  to  be  put. 
Reservoir  basins  have  been  classified  according  to  their  location 
as  follows : 

1.  Natural  lakes. 

2.  Natural  depressions  on  main  drainage  lines. 

3.  Natural  depressions  on  lateral  drainage  lines. 

4.  Arbitrary  and  artificially  constructed  basins. 

Natural  lakes  may  need  to  be  investigated  more  or  less  thorough- 
ly to  determine  the  character  of  their  waters,  whether  saline,  alka- 
line or  fresh.  It  may  also  be  necessary  to  know  their  normal  depth 
and  capacity,  and  to  make  a  study  of  their  outlet  if  they  have  one. 
In  some  instances  the  storage  capacity  of  a  lake  may  be  enormous- 
ly increased  by  means  of  a  comparatively  low  and  inexpensive  em- 
bankment. 

The  area  of  reservoir  basin,  mean  depth,  temperature  of  the 
water,  exposure  of  wind  and  sunshine,  losses  by  seepage  and  evap- 
oration, all  have  a  bearing  upon  the  available  water  supply  and  in- 
fluence the  design  of  the  dam  and  accessories  to  the  reservoir. 

In  determining  the  character  and  suitability  of  materials  for  con- 
structing a  dam  it  is  necesary  to  make  a  careful  study  of  the  soil 
and  geological  formation.  This  is  best  accomplished  by  digging 
numerous  test  pits  over  the  basin,  especially  in  the  vicinity  of  the 
proposed  dam  site ;  borings  alone  should  never  be  relied  upon  for 
this  information.  For  such  an  investigation  the  advisability  of  bor- 
rowing material  for  dam  construction  from  the  reservoir  basin  is 


6  EARTH  DAMS. 

determined.  The  porous  character  of  the  subsoil  strata,  or  the 
dip  and  nature  of  the  bed  rock,  may  forbid  the  removal  of  material 
from  the  floor  of  the  basin,  even  at  a  remote  distance  from  the  dam 
site. 

The  area  to  be  flooded  should  be  cleared  and  grubbed  more  or 
less  thoroughly,  depending  again  upon  the  use  for  which  the  water 
is  impounded.  In  no  instance  should  timber  be  left  standing  below 
the  high  water  level  of  the  reservoir ;  and  all  rubbish  liable  to  float 
and  obstruct  the  outlet  tunnel  and  spillway  during  a  time  of  flood 
should  be  removed. 

The  accessories  to  a  reservoir,  to  which  reference  has  been  made, 
may  be  enumerated  as  follows : 

1.  Outlet  pipes  or  tunnel. 

2.  Gate  tower,  screens  and  controlling  devices. 

3.  Sluiceways  for  silt  or  sand. 

4.  Wasteway  channel  or  weir. 

5.  Cover,  settling  basin,  aerating  devices,  etc. 

Some  of  these  are  necessary  and  common  to  all  classes  of  reser- 
voirs, while  others  are  employed  only  in  special  cases,  as  for 
domestic  water  supplies.  All  reservoirs  formed  by  earth  embank- 
ments must  have  at  least  two  of  these,  namely  a  wasteway,  which 
is  its  safety  valve,  and  outlet  pipes  or  outlet  tunnel. 

It  may  be  stated  that  the  proper  location  and  construction  of 
the  outlet  for  a  reservoir  are  of  vital  importance,  since  either  to 
improper  location  or  faulty  construction  may  be  traced  most  of  the 
failures  of  the  past.  It  is  almost  impossible  to  prevent  water 
under  high  pressure  from  following  along  pipes  and  culverts  when 
placed  in  an  earth  dam.  The  pipes  and  culverts  frequently  leak, 
and  failure  ensues.  Failure  may  result  from  one  or  more  of  the 
following  causes : 

1.  By  improper  design  and  placement  of  the  pudddle  around  the 
pipes. 

2.  By  resting  the  pipes  upon  piers  of  masonry  without  continu- 
ous longitudinal  support. 

3.  By  reason  of  subsidence  in  the  cuts  of  the  embankments  and 
at  the  core  walls,  due  to  the  great  weight  at  these  points. 

4.  Leakage  due  to  inherent  defects,  frost,  deterioration,  etc. 

Mr.  Beardsmore,  the  eminent  English  engineer  who  built  the 
Dale  Dyke  embankment  at  Sheffield  which  failed  in  1864,  and  who 
was  afterwards  requested  to  study  and  report  upon  the  great  reser- 
voirs in  Yorkshire  and  Lancashire,  said,  after  examination  and  care- 


PRELIMINARY  STUDIES  AND  INVESTIGATIONS.  7 

ful  study  of  reservoir  embankment  construction,  that  "in  his  opin- 
ion there  were  no  conditions  requiring  that  a  culvert  or  pipes 
should  be  carried  through  any  portion  of  the  made  bank."  The 
writer  would  go  even  further  and  say  that  the  only  admissable  out- 
let for  a  storage  reservoir  formed  by  a  high  earth  dam  is  some 
form  of  tunnel  through  the  natural  formation  at  a  safe  distance 
from  the  embankment. 

Dam   Site. 

The  third  preliminary  study  (that  relating  to  the  dam  site  itself) 
will  be  considered  under  three  heads : 

1.  Location. 

2.  Physical  features,  materials,  etc. 

3.  Foundation. 

LOCATION. — The  location  for  a  dam  is  generally  determined 
by  the  use  which  is  to  be  made  of  it,  or  by  the  natural  advantages 
for  storage  wrhich  it  may  possess.  If  it  be  for  water  power  it  is 
very  frequently  located  upon  the  main  stream  at  the  point  of  great- 
est declivity.  If  for  storage  it  may  be,  as  we  have  seen,  at  the 
head  of  a  river  system,  on  one  of  its  tributaries,  or  in  a  valley 
lower  down. 

The  type  of  dam  which  should  be  built  at  any  particular  local- 
ity involves  a  thorough  knowledge,  not  alone  of  the  catchment-area 
and  reservoir  basin,  but  also  accurate  information  regarding  the 
geology  of  the  dam  site  itself.  It  would  be  very  unwise  to  decide 
definitely  upon  any  particular  type  of  dam  without  first  obtaining 
such  information.  Too  frequently  has  this  been  done,  causing 
great  trouble  and  expense,  if  not  resulting  in  a  total  failure  of  the 
dam. 

The  conditions  favorable  for  an  earth  dam  are  usually  unfavor- 
able for  a  masonry  structure,  and  vice  versa.  Again,  there  may 
be  local  conditions  requiring  some  entirely  different  type. 

Dams  situated  upon  the  main  drainage  lines  of  large  catchment 
areas  are  usually  built  of  stone  or  concrete  masonry,  and  designed 
with  large  sluiceways  and  spillways  for  the  discharge  both  of  silt 
and  flood  waters.  It  need  scarcely  be  remarked  that,  as  a  rule,  such 
sites  are  wholly  unsuited  to  earthwork  construction.  It  is  said, 
however,  that  "every  rule  has  at  least  one  exception,"  and  this  may 
be  true  of  those  relating  to  dam  sites,  as  will  appear  later  under 
the  head  of  new  types. 

In  a  general  way,  the  location  of  high  earth  dams  is  governed 


g  EARTH  DAMS. 

by  the  configuration  of  the  ground  forming  the  storage  basin.  It 
may  not  be  possible,  however,  to  decide  upon  the  best  available  site 
without  careful  preliminary  surveys  and  examinations  of  the  geo- 
logical formation. 

All  earth  dams  must  be  provided  with  a  wasteway,  ample  to  dis- 
charge the  maximum  flood  tributary  to  the  reservoir.  Whatever 
type  of  wasteway  be  adopted,  no  reliance  should  ever  be  put  upon 
the  outlet  pipes  for  this  purpose.  The  outlet  should  only  figure  as 
a  factor  of  safety  for  the  wasteway,  insuring,  as  it  were,  the  accuracy 
of  the  estimated  flood  discharge.  The  safety  of  the  dam  demands 
that  ample  provision  be  made  for  a  volume  of  water  in  excess  of 
normal  flood  discharge.  This  most  necessary  adjunct  of  earth 
dams  may  be  an  open  channel,  cut  through  the  rim  of  the  reservoir 
basin,  discharging  into  a  side  ravine  which  enters  the  main  drainage 
way  some  distance  below  the  dam.  It  may  be  necessary  and  possi- 
ble to  pierce  the  rim  by  means  of  a  tunnel  where  its  length  would 
not  prohibit  such  a  design.  Lastly,  there  may  be  no  other  alter- 
native than  the  construction  of  an  overfall  spillway,  at  one  or  both 
ends  of  the  embankment.  This  last  method  is  the  least  desirable 
of  any  and  should  be  resorted  to  only  when  the  others  are  imprac- 
ticable ;  even  then,  the  volume  of  water,  local  topography,  geology, 
and  constructive  materials  at  hand  must  be  favorable  to  such  a 
design.  If  they  are  not  favorable  it  may  be  asked,  "what  then?'* 
Simply  do  not  attempt  to  build  an  earth  dam  at  this  site. 

PHYSICAL  FEATURES,  MATERIALS,  ETC.— An  investiga- 
tion of  the  location  and  the  physical  features  of  the  dam  site  should 
include  a  careful  and  scientific  examination  of  the  materials  in  the 
vicinity,  to  determine  their  suitability  for  use  in  construction.  An 
earth  embankment  cannot  be  built  without  earth,  and  an  earth 
dam  cannot  be  built  with  safety  without  the  right  kind  of  earth 
material. 

Test  pits  judiciously  distributed  and  situated  at  different  eleva- 
tions will  indicate  whether  there  is  a  sufficient  amount  of  suitable 
material  within  a  reasonable  distance  of  the  dam.  The  type  of  earth 
dam  best  suited  for  any  particular  locality,  and  its  estimated  cost, 
are  thus  seen  to  depend  upon  the  data  and  information  obtained 
by  these  preliminary  studies.  Economical  construction  requires 
the  use  of  improved  machinery  and  modern  methods  of  Handling 
materials,  but  far  more  important  even  than  these  are  the  details  of 
construction. 


PRELIMINARY  STUDIES  AND  INVESTIGATIONS.  9 

FOUNDATION. — We  may  now  assume  that  our  preliminary 
studies  relating  to  the  location  and  physical  features  of  the  dam 
site  are  satisfactory.  We  must  next  investigate  the  foundation  up- 
on which  the  dam  is  to  be  built.  This  investigation  is  sometimes 
wholly  neglected  or  else  done  in  such  a  way  as  to  be  practically 
useless.  To  merely  drive  down  iron  rods  feeling  for  so-called  bed 
rock,  or  to  make  only  a  few  bore-holes  with  an  earth  auger  should 
in  no  instance  be  considered  sufficient.  Borings  may  be  found 
necessary  at  considerable  depths  below  the  surface  and  in  certain 
classes  of  material,  but  dug  pits  or  shafts  should  always  be  re- 
sorted to  for  moderate  depths  and  whenever  practicable.  Only  by 
such  means  may  the  true  character  of  the  strata  underlying  the 
surface,  and  the  nature  and  condition  of  the  bed  rock,  if  it  be 
reached,  become  known.  If  a  satisfactory  stratum  of  impermeable 
material  be  found  it  is  necesary  also  to  learn  both  its  thickness  and 
extent.  It  may  prove  to  be  only  a  "pocket"  of  limited  volume,  or 
if  found  to  extend  entirely  across  the  depression  lengthwise  of  the 
dam  site  it  may  "pinch  out''  on  lines  transversely  above  or  below. 
Shafts  and  borings  made  in  the  reservoir  basin  and  below  the  dam 
site  will  determine  its  extent  in  this  direction,  knowledge  of  which 
is  very  important. 

Fig.  i,  showing  a  longitudinal  section  of  the  site  of  the  Yarrow 
Dam  of  the  Liverpool  Water-Works,  England,  illustrates  the  neces- 
sity of  such  investigation.  A  bore  hole  at  station  2  +  00  met  a  large 
boulder  which  at  first  was  erroneously  thought  to  be  bed  rock. 
The  hole  at  station  3  +  50  met  a  stratum  of  clay  which  proved  to 
be  only  a  pocket. 

The  relative  elevation  of  the  different  strata  and  of  the  bed  rock 
formation,  referred  to  one  common  datum,  should  always  be  deter- 
mined. These  elevations  will  indicate  both  the  dip  and  strike  of  the 
rock  formation  and  are  necessary  for  estimating  the  quantities  of 
material  to  be  excavated  and  removed,  including  estimates  of  cost. 
They  furnish  information  of  value  in  determining  the  rate  of  perco- 
lation or  filtration  through  the  different  classes  of  material  and 
the  amount  of  probable  seepage,  as  will  appear  later.  The  cost 
cf  excavating,  draining  and  preparing  the  floor  or  foundation  for 
a  dam  is  often  very  great,  amounting  to  20  or  30%  of  the  total  cost. 

Fig.  2  is  a  transverse  section  of  the  Yarrow  Dam.  This  partic- 
ular dam  has  been  selected  as  fairly  representative  of  English  prac- 
tice and  of  typical  design.  It  is  one  of  the  most  widely  known  earth 
clams  in  existence. 


IO 


EARTH  DAMS. 


PRELIMINARY  STUDIES  AND  INVESTIGATIONS.  n 

At  the  Yarrow  dam  site  it  was  necessary  to  go  97  ft.  below  the 
original  surface  to  obtain  a  satisfactory  formation  or  one  that  was 
impermeable.  A  central  trench  was  excavated  to  bed  rock,  par- 
allel to  the  axis  of  the  dam,  and  filled  with  clay  puddle  to  form  a 
water-tight  connection  with  the  rock,  and  prevent  the  water  in  the 
reservoir  from  passing  through  the  porous  materials  under  the 
body  of  the  embankment.  This  interesting  dam  will  be  more  fully 
described  later,  when  the  different  types  of  earth  dams  are  dis- 
cussed. 


CHAPTER  III. 
Outline  Study  of  Soils.     Puddle. 

The  following  study  of  soils  is  merely  suggestive  and  is  here 
given  to  emphasize  the  importance  of  the  subject,  at  the  risk  of 
being  considered  a  digression.  Soil  formations  are  made  in  one 
of  three  ways: 

1.  By  decomposition  of  exposed  rocks. 

2.  By  transportation  or  sedimentation  of  fine  and  coarse  mater- 
ials worn  from  rocks. 

3.  By  transformation  into  humus  of  decayed  organic  matter. 
The  transforming  agencies  by  which  soils  succeed  rocks  in  geo- 
logical progression  have  been  classified  as  follows : 

1.  Changes  of  temperature. 

2.  Water. 

3.  Air. 

4.  Organic  life. 

Heat  and  its  counter  agent  frost  are  the  most  powerful  forces  in 
nature,  their  sensible  physical  effects  being  the  expansion  and  con- 
traction of  matter. 

Water  has  two  modes  of  action,  physical  and  chemical.  This 
agent  is  the  great  destroyer  of  the  important  forces,  cohesion  and 
friction.  Cohesion  is  a  force  uniting  particles  of  matter  and  resists 
their  separation  when  the  motion  attempted  is  perpendicular  to  the 
plane  of  contact.  Friction  is  a  force  resisting  the  separation  of 
surfaces  when  motion  is  attempted  which  produces  sliding.  The 
hydrostatic  pressure  and  resultant  effect  upon  submerged  surfaces 
need  to  be  kept  constantly  in  mind.  When  the  surface  is  imper- 
meable the  line  of  pressure  is  normal  to  its  plane,  but  when  once 
saturated  there  are  also  horizontal  and  vertical  lines  of  pressure. 
Since  the  strength  of  an  earth  dam  depends  upon  two  factors, 
namely,  its  weight  and  frictional  resistance  to  sliding,  the  effect  of 
water  upon  different  materials  entering  into  an  earth  structure 
should  be  most  carefully  considered.  This  will  therefore  occupy  a 
large  place  in  these  pages.  An  earth  embankment  founded  upon 
reck  may  become  saturated  by  water  forced  up  into  it  from  below 
through  cracks  and  fissures,  reducing  its  lower  stratum  to  a  state 


OUTLINE  STUDY  OF  SOILS.  13 

of  muddy  sludge,  on  which  the  upper  part,  however  sound  in  itself, 
would  slide.  The  best  preliminary  step  to  take  in  such  a  case  is 
to  intersect  the  whole  site  with  wide,  dry,  stone  drains,  their  depths 
varying  according  to  the  nature  of  the  ground  or  rock. 

Air  contains  two  ingredients  ever  active  in  the  process  of  decom- 
position, carbonic  acid  and  oxygen. 

Organic  Life  accomplishes  its  decomposing  effect  both  by  physi- 
cal and  chemical  means.  The  effect  of  organic  matter  upon  the 
mineral  ingredients  of  the  soil  may  be  stated  as  follows  : 

1.  By  their  hydroscopic  properties  they  keep  the  soil  moist. 

2.  Their  decomoosition  yields  carbonic  acid  gas. 

3.  The  acids  produced  disintegrate  the  mineral  constituents,  re- 
ducing insoluble  matter  to  soluble  plant  food. 

4.  Nitric  acid  results   in  nitrates,  which  are  the  most  valuable 
form"  of  nutritive  nitrogen,  while  ammonia  and  the  other  salts  that 
are  formed  are  themselves  direct  food  for  plants. 

Vegetable  Huimis  is  not  the  end  of  decomposition  of  organic  mat- 
ter, but  an  intermediate  state  of  transformation.  Decay  is  a  pro- 
cess almost  identical  with  combustion,  where  the  products  are  the 
same,  and  the  end  is  the  formation  of  water  and  carbonic  acid,  with 
a  residue  of  mineral  ash.  The  conditions  essential  to  organic  de- 
composition are  also  those  most  favorable  to  combustion  or  oxida- 
tion, being  (i)  access  of  air,  (2)  presence  of  moisture,  and  (3)  appli- 
cation of  heat. 

Now  the  cooperation  of  these  chemical  and  physical  forces,  which 
are  ever  active,  is  called  "weathering."  .  Slate  rock,  for  instance, 
weathers  to  clay,  being  impregnated  with  particles  of  mica,  quartz, 
chlorite  and  hornblend.  Shales  also  weather  to  clay,  resulting  of- 
ten in  a  type  of  earth  which  is  little  more  than  silicate  of  aluminum 
with  iron  oxide  and  sand. 

In  the  vicinity  of  the  Tabeaud  Dam,  recently  built  under  the  per- 
sonal supervision  of  the  author,  the  construction  of  which  will  be 
described  later,  there  is  to  be  found  a  species  of  potash  mica,  which 
in  decomposing  yields  a  yellow  clay  (being  ochre-colored  from  the 
presence  of  iron),  mixed  with  particles  of  undecomposed  mica.  This 
material  is  subject  to  expansion,  and  by  reason  of  its  lack  of  grit 
and  its  unctuous  character  it  was  rejected  or  used  very  sparingly. 
Analysis  of  this  material  gave,  Silica,  54.1  to  59.5%  ;  potash,  1.5  to 
2.3%;  soda,  2.7  to  3.7%. 

Soil  analysis  may  be  either  mechanical  or  chemical.  For  pur- 
poses of  earthwork,  we  are  most  interested  in  the  former,  having  to 


I4  EARTH  DAMS. 

deal  with  the  physical  properties  of  matter.  Chemical  analysis, 
however,  will  often  afford  information  of  great  value  regarding  cer- 
tain materials  entering  into  the  construction  of  earth  dams.  The 
most  important  physical  properties  are : 

(1)  Weight  and  specific  gravity. 

(2)  Coefficient  of  friction  and  angle  of  repose. 

(3)  Structure  and  coloring  ingredients. 

(4)  Behavior  toward  water. 

There  are  two  distinct  methods  of  mechanical  analysis :  (i)  Gran- 
ulating with  sieves,  having  round  holes.  (2)  Elutriating  with  water, 
the  process  being  known  as  silt  analysis. 

It  would  require  a  large  volume  to  present  the  subject  of  soil 
analysis  in  any  way  commensurate  with  its  importance.  Experi- 
ments bearing  upon  the  subjects  of  imbibition,  permeability,  capil- 
larity, absorption  and  evaporation,  of  different  earth  materials,  are 
equally  interesting  and  important.* 

The  permeability  of  soils  will  be  discussed  incidentally  in  connec- 
tion with  certain  infiltration  experiments  to  be  given  later. 

Puddle. 

Puddle  without  qualification  may  be  defined  as  clayey  and  grav- 
elly earth  thoroughly  wetted  and  mixed,  having  a  consistency 
of  stiff  mud  or  mortar.  Puddle  in  which  the  predominating  in- 
gredient of  the  mixture  is  pure  clay,  is  called  clay  puddle.  Gravel 
puddle  contains  a  much  higher  percentage  of  grit  and  gravel  than 
the  last-named  and  yet  is  supposed  to  have  enough  clayey  mater- 
ial to  bind  the  matrix  together  and  to  fill  all  the  voids  in  the 
gravel. 

The  term  earthen  concrete  may  also  be  applied  to  this  class  of 
material,  especially  when  only  a  small  quantity  of  water  is  used 
in  the  mixture.  These  different  kinds  of  puddling  materials  may 
be  found  in  natural  deposits  ready  for  use,  only  requiring  the 
addition  of  the  proper  amount  of  water.  It  is  usually  necessary, 
however,  to  mix,  artificially,  or  combine  the  different  ingredients 
in  order  to  obtain  the  right  proportions.  Some  engineers  think 
grinding  in  a  pug-mill  absolutely  essential  to  obtain  satisfactory 
results. 

Puddle  is  handled  very  much  as  cement  concrete,  which  is  so 

*The  writer  had  intended  to  present  a  table  of  physical  properties  of  different  ma- 
terials, giving  their  specific  gravity,  weight,  coefficient  of  friction,  angle  of  repose, 
percentage  of  imbibition,  percentage  of  voids,  etc.,  but  found  it  impossible  to  harmo- 
nize the  various  classifications  of  materials  given  by  different  authorities. 


OUTLINE  STUDY  OF  SOILS'.       £  }         X5 

well  understood  that  detailed  description  is  hardly~necessary.  In- 
stead of  tampers,  sharp  cutting  implements  are  usually  employed 
in  putting  puddle  into  place.  Trampling  with  hoofed  animals  is 
frequently  resorted  to,  both  for  the  purpose  of  mixing  and  com- 
pacting. 

As  has  been  stated,  clays  come  from  the  decomposition  of  crys- 
taline  rocks.  The  purest  clay  known  (kaolin)  is  composed  of 
alumina,  silica  and  water.  The  smaller  the  proportion  of  silica 
the  more  water  it  will  absorb  and  retain.  Dry  clay  will  absorb 
nearly  one-third  of  its  weight  of  water,  and  clay  in  a  naturally 
moist  condition  1-6  to  1-8  its  weight  of  water.  The  eminent 
English  engineers,  Baker  and  Latham,  put  the  percentage  of  ab- 
sorption by  clayey  soils  as  high  as  40  to  60%.  Pure  clays  shrink 
about  5%  in  drying,  while  a  mixture  by  weight  of  I  clay  to  2 
sand  will  shrink  about  3%.  It  follows,  then,  that  the  larger  the 
percentage  of  clay  there  may  be  in  a  mixture  the  greater  will 
be  both  the  expansion  and  the  contraction. 

Clay  materials  may  be  very  deceptive  in  some  of  their  physical 
properties,  being  hard  to  pick  under  certain  conditions,  and  yet 
when  exposed  to  air  and  water  will  rapidly  disintegrate.  Beds  of 
clay,  marl  and  very  fine  sand  are  liable  to  slip  when  saturated, 
becoming  semi-fluid  in  their  nature,  and  will  run  like  cream. 

The  cohesive  and  frictional  resistances  of  clays  becoming  thus 
very  much  reduced  when  charged  with  water,  a  too  liberal  use  of 
this  material  is  to  be  deprecated.  The  ultimate  particles  forming 
clays,  viewed  under  the  microscope,  are  seen  to  be  flat  and  scale- 
like,  while  those  of  sands  are  more  cubical  and  spherical.  This  is 
a  mechanical  difference  which  ought  to  be  apparent  to  even  a 
superficial  observer  and  yet  has  escaped  recognition  by  many  who 
have  vainly  attempted  a  definition  of  quicksand. 

Mr.  Strange  recommends  filling  the  puddle  trench  with  mater- 
ial having  three  parts  soil  and  two  parts  sand.  After  the  first 
layer  next  to  bed  rock  foundation,  which  he  kneads  and  compacts, 
he  would  put  the  layers  in  dry,  then  water  and  work  it  by  tread- 
ing, finally  covering  to  avoid  its  drying  out  and  cracking. 

Prof.  Philipp  Forchheimer,  of  Gratz,  Austria,  one  of  the  high- 
est authorities  and  experimentalists,  affirms  that  if  a  sandy  soil 
contains  clay  to  such  an  extent  that  the  clay  fills  up  the  inter- 
stices between  the  grains  of  sand  entirely  the  compound  is  pract- 
ically impervious. 

Mr.  Herbert  M.  Wilson,  C.  E.,  in  his  "Manual  of  Irrigation  En- 


!6  EARTH  DAMS. 

gineering,"   recommends   the    following   as    an    ideal    mixture    of 
materials : 

Cn.  yds.  Cu.  yds. 

Coarse  gravel i.oo  Clay 0.20 

Fine  gravel 0.35 

Sand 0.15  Total   1.70 

This  mixture,  when  rolled  and  compacted,  should  give  1.25  cu. 
yds.  in  bulk,  thus  resulting  in  26^%  compression. 

Mr.  Clemens  Herschel  suggests  the  following  test  of  "good  bind- 
ing gravel :"  "Mix  with  water  in  a  pail  to  the  consistency  of  moist 
earth ;  if  on  turning  the  pail  upside  down  the  gravel  remains  in  the 
pail  it  is  fit  for  use,  otherwise  it  is  to  be  rejected."  For  puddling 
material  he  would  use  such  a  proportion  as  will  render  the  water 
invisible. 


CHAPTER  IV. 
The  Tabeaud  Dam,  California. 

The  Tabeaud  Dam,  in  Amador  County,  Cal./built  under  the 
supervision  of  the  author  for  the  Standard  Electric  Co.^ds  an  ex- 
ample of  the  homogeneous  earth  dam.  A  somewhat  fuller  descrip- 
tion and  discussion  will  be  given  of  this  dam  than  of  any  other,  not 
on  account  of  its  greater  importance  or  interest,  but  because  it  ex- 


Mining 
Reservoir 


FIG.  3.— PLAN  OF    TABEAUD  (RESERVOIR,  WITH    CONTOURS. 

emplifies  certain  principles  of  construction  upon  which  it  is  desired 
to  put  special  emphasis.  This  dam  was  described  in  Engineering 
News  of  July  10,  1902,  to  which  the  reader  is  referred  for  more 
complete  information  than  is  given  here. 

Fig.  3  is  a  contour  map  of  the  Tabeaud  Reservoir,  showing  the 
relative  locations  of  the  dam,  wasteway  and  outlet  tunnel.  Fig.  4 
shows  the  bed  rock  drainage  system  and  the  letters  upon  the  draw- 


i8 


EARTH  DAMS. 


Strean 


Stream 


PIG.  l.-^PLAN    OF    TABEJAUD    DAM,    SHOWING    BED  ROCK  DRAINAGE   SYSTEM. 


ROCK         Drain.  Interior          Puddle          Trench. 

FIG.  5.— 'DETAILS   OF  BED  ROCK  DRAINS  AT  THE    TABEAUD  DAM. 


THE  TABEAUD  DAM.  IOy 

ing  will  assist  in  following  the  explanation  given  in  the  text.  The 
whole  up-stream  half  of  the  dam  site  was  stripped  to  bed  rock.  As 
the  work  of  excavation  advanced  pockets  of  loose  alluvial  soil  were 
encountered,  which  were  suggestive  of  a  refill,  possibly  the  result 
of  placer  mining  operations  during  the  early  mining  days  of  Califor- 
nia. In  addition  to  this  were  found  thin  strata  ot  sand  and  gravel 
deposited  in  an  unconformable  manner.  The  slate  bed  rock  near 
the  up-stream  toe  of  the  dam  was  badly  fissured  and  yielded  consid- 
erable water.  A  quartz  vein  from  I  to  2  ft.  in  thickness  crossed  the 
dam  site  about  150  ft.  above  the  axis  of  the  dam.  The  slate  rock 


FIG.  6.— VIEW   OF  BED  ROCK  TRENCHES,   TAB'EAUD   DAM. 

above  this  vein  or  fault  line  was  quite  variable  in  hardness    and 
dipped  at  an  angle  of  40  degrees  toward  the  reservoir. 

The  rear  drain  terminates  at  a  weir  box  (Z)  outside  of  the  down- 
stream slope  at  a  distance  of  500  ft.  from  the  axis  of  the  dam.  This 
drain  branches  at  the  down-stream  side  of  the  central  trench,  (Y), 
one  branch  being  carried  up  the  hillside  to  high-water  level  (W)  at 
the  North  end  of  the  dam,  and  the  other  to  the  same  elevation  at  the 
South  end  (X). 


20  V  EARTH  DAMS. 

Fig.  5  shows  how  these  drains  were  constructed.  After  the  re- 
moval of  all  surface  soil  and  loose  rock,  a  trench  5  to  10  ft.  wide 
was  cut  into  the  solid  rock,  the  depth  of  cutting  varying  with  the 
character  of  the  bed  rock.  Upon  the  floor  of  this  trench  a  small 
open  drain  was  made  by  notching  the  bed  rock  and  by  means  of 
selected  stones  of  suitable  size  and  hardness.  The  stringers  and 
cap-stones  were  carefully  selected  and  laid,  so  that  no  undue  settle- 
ment or  displacement  might  occur  by  reason  of  the  superincumbent 


FIG.    7.— VIEW    OF  NORTH   TRENCH,   TABEAUD   DAM. 

weight  of  the  dam.  All  crevices  were  carefully  filled  with  spawls 
and  the  whole  overlaid  18  ins.  in  depth  with  broken  stone  I  to  3 
ins.  in  diameter.  Upon  this  layer  of  broken  stone  and  fine  gravel 
was  deposited  choice  clay  puddle,  thoroughly  wetted  and  com- 
pacted, refilling  the  trenches. 

These  drains  served  a  useful  purpose  during  construction,  in 
drying  off  the  surface  of  the  dam  after  rains.  The  saturation  of  the 
outer  slope  of  the  dam  by  water  creeping  along  the  line  of  contact 


THE  TABEAUD  DAM. 


FIG.  8.— VIEW  OF  SOUTH  TRENCH,  TABEAUD  DAM. 


FIG.  9. -VIEW  OF  MAIN  CENTRAL  DRAIN,  TABEAUD  DAM. 


22 


EARTH  DAMS. 


should  thus  be  prevented,  and  the  integrity  or  freedom  from  sat- 
uration of  the  down-stream  half  should  be  preserved.  It  is  be- 
lieved that  the  puddle  overlying  these  rock  drains  will  effectually 
prevent  any  water  from  entering  the  body  of  the  embankment  by 
upward  pressure  and  that  the  drains  will  thus  forever  act  as  ef- 
ficient safeguards. 

The  main  drain  was  extended,  temporarily  during  construction, 
from  the  central  trench  (Fig.  4),  to  the  up-stream  toe  of  the  dam. 
This  was  cut  5  or  6  ft.  deep  into  solid  rock,  below  the  general 
level  of  the  stripped  surface.  Fig.  6  is  reproduced  from  a  photo- 
graph of  this  trench.  An  iron  pipe  2  ins.  in  diameter  was  im- 
bedded in  Portland  cement  mortar  and  concrete,  and  laid  near 
the  bottom  of  the  trench. 

At  the  point  (B)  where  the  quartz  vein  (already  described)  in- 
tersected this  drain,  two  branch  drains  were  made,  following  the 
fault  well  into  the  hill  on  both  sides.  Figs.  7  and  8  are  views 
of  the  North  and  South  trenches,  respectively.  These  trenches 
were  necessary  to  take  care  of  the  springs  issuing  along  the 
quartz  vein.  This  water  led  to  a  point  (N,  Fig.  4)  near  the  up- 
stream toe,  by  means  of  the  drain  shown  in  Fig.  9. 

The  lateral  drains  and  that  portion  of  the  main  central  drain 
extending  from  their  junction  (B)  to  a  point  (N)  about  230  ft. 
from  the  axis  of  the  dam  have  pieces  of  angle  iron  or  wooden 
Y-fluming  laid  on  the  bottom  of  the  trenches  immediately  over 
the  2-in.  pipe,  as  shown  in  Figs.  7,  8  and  9.  These  are  covered  in 
turn  with  Portland  cement  mortar,  concrete,  clay  puddle  and 
earth  fill.  The  water  will  naturally  flow  along  the  line  of  least  re- 
sistance, and  consequently  will  follow7  along  the  open  space  be- 
tween the  angle  irons  and  the  outside  of  the  pipe  until  it  reaches 
the  chamber  and  opening  in  the  pipe,  permitting  the  water  to  enter 
and  be  conveyed  through  the  imbedded  pipe  line  to  the  rear  drain. 
This  point  of  entry  is  a  small  chamber  in  a  solid  cross-wall  of  rich 
cement  mortar,  and  is  the  only  point  where  water  can  enter  this 
pipe  line,  the  two  branches  entering  the  wells  and  the  stand-pipe 
at  their  junction  (soon  to  be  described)  having  been  closed. 

That  portion  of  the  foundation  between  the  axis  of  the  dam  and 
the  quartz  vein,  a  distance  of  about  160  ft.,  was  very  satisfactory, 
without  fissures  or  springs  of  water.  In  this  portion  the  2-in. 
pipe  was  imbedded  in  mortar  and  concrete  without  angle  irons, 
and  the  continuitv  of  the  trench  broken  by  numerous  cross- 
trenches  cut  into  the  rock  and  filled  with  concrete  and  puddle.  It 


THE  TABEAUD  DAM. 


24  EARTH  DAMS. 

is  believed  that  no  seepage  water  will  ever  pass  through  this  por- 
tion of  the  dam.  If  any  should  ever  find  its  way  under  the  puddle 
and  through  the  bed  rock  formation,  the  rear  drain,  with  its  hill- 
side branches,  will  carry  it  away  and  prevent  the  saturation  of  the 
lower  or  down-stream  half  of  the  dam. 

At  the  up-stream  toe  of  the  embankment,  two  wells  or  sumps 
(shown  at  "S"  and  "K,"  Fig.  4)  were  cut  10  or  12  ft.  deeper  than 
the  main  trench,  which  received  the  water  entering  the  inner  toe 
puddle  trench  during  construction.  This  water  was  disposed  of 
partly  by  pumping  and  partly  by  means  of  the  2-in.  branch  pipes 
leading  into  and  from  these  wells.  At  their  junction  (J)  a  2-in. 
stand-pipe  was  erected,  which  was  carried  vertically  up  through 
the  embankment,  and  finally  filled  with  cement.  The  branch  pipes 
from  the  wells  were  finally  capped  and  the  wells  filled  with  broken 
stone,  as  previously  mentioned. 

EMBANKMENT. — As  has  been  said,  the  upper  surface  of  the 
slate  bed  rock  was  found  to  be  badly  fissured,  especially  near  the 
upstream  toe  of  the  dam,  and  as  the  average  depth  below  the  sur- 
face of  the  ground  was  not  very  great,  it  was  thought  best  to  lay 
bare  the  bed  rock  over  the  entire  upper  half  of  the  dam  site.  Had 
the  depth  been  much  greater,  it  would  have  been  more  economical 
and  possibly  sufficient  to  have  put  reliance  in  a  puddle  trench, 
alone,  for  securing  a  water-tight  connection  between  the  founda- 
tion and  the  body  of  the  dam. 

At  the  axis  of  the  dam  and  near  the  inner  toe,  where  the  puddle 
walls  abutted  against  the  hillsides,  the  excavation  always  ex- 
tended to  bed  rock.  Vertical  steps  and  offsets  were  avoided  and 
the  cuts  were  made  large  enough  for  horses  to  turn  in  while 
tramping,  these  animals  being  used,  singly  and  in  groups,  to  mix 
and  compact  the  puddle  and  thus  lessen  the  labor  of  tamping  by 
hand.  In  plan,  the  hillside  contact  of  natural  and  artificial  sur- 
faces presents  a  series  of  corrugated  lines,  (as  is  clearly  shown  in 
Fig.  4.  >  After  all  loose  and  porous  materials  had  been  -removed, 
the  stripped  surface  and  the  slopes  of  all  excavations  were  thor- 
oughly -wetted  from  time  to  time  by  means  of  hose  and  nozzle,  the 
water  being  delivered  under  pressure.  Fig.  10  is  a  view  of  the 
dam  taken  when  it  was  about  half  finished  and  shows  the  work 
in  progress. 

The  face  puddle  shown  in  Fig.  n  was  used  merely  to  "make 
assurance  doubly  sure"  and  was  not  carried  entirely  up  to  the 
top  of  the  dam.  The  earth  of  which  the  dam  was  constructed  mav 


THE    TABEAUD   DAM.  25 

be  described  as  a  red  gravelly  clay,  and  in  the  judgment  of  the 
author  is  almost  ideal  material  for  the  purpose.  Physical  tests 
and  experiments  made  with  the  materials  at  different  times  during 
construction  gave  the  following  average  results : 

Pounds. 

Weight  of      cu.  ft.  earth,  dust  dry 84.0 

"        saturated  earth  101.8 

"        moist  loose  earth  76.6 

"        loose  material  taken  from  test  pits  on  the  dam        80.0 

"       earth  in  place  taken  from  the  borrow  pits 116.5 

"       earth  material  taken  from  test-pits  on  the  dam.      133.0 

Per  cent. 

Percentage  of  moisture  in  natural  earth 19 

"  voids  in  natural  earth 52 

"  "  grit  and  gravel  in  natural  earth 38 

u  compression  on  dam  over  earth  at  borrow-pit 16 

"  compression  on  dam  over  earth  in  wagons 43 

Degrees. 

Angle  of  repose  of  natural  moist  earth  44 

Angle  of  repose  of  earth,  dust  dry -. -.      36 

Angle  of  repose  of  saturated  earth 23 

CONSTRUCTION  DETAILS.— The  materials  forming  the  bulk 
of  the  dam  were  hauled  by  four-horse  teams,  in  dump-wagons, 
holding  3  cu.  yds.  each.  The  wagons  loaded  weighed  about  six 
tons  and  were  provided  with  two  swinging  bottom-doors,  which 
the  driver  could  operate  with  a  lever,  enabling  the  load  to  be 
quickly  dropped  while  the  team  was  in  motion.  If  the  material 
was  quite  dry,  the  load  could  be  dumped  in  a  long  row  when  so 
desired. 

After  plowing  the  surface  of  the  ground  and  wasting  any  objec- 
tionable surface  soil,  the.  material  was  brought  to  common  earth- 
traps  for  loading  into  wagons,  by  buck  or  dragscrapers  of  the 
Fresno  pattern.  In  good  material  one  trap  with  eight  Fresno- 
scraper  teams  could  fill  25  wagons  per  hour.  The  average  length 
of  haul  for  the  entire  work  was  about  1,320  ft. 

The  original  plans  and  specifications  were  adhered  to  through- 
out, with  the  single  exception  that  the  central  puddle  wall  was  not 
carried  above  elevation  1,160,  as  shown  on  Figs,  n  and  12,  more 
attention  being  given  to  the  inner  face  puddle.  This  modification 
in  the  original  plans  was  made  because  of  the  character  of  the  ma- 
terials available  and  the  excellent  results  obtained  in  securing  an 
homogeneous  earthen-concrete,  practically  impervious. 


\ 


EARTH  DAMS. 


The  top  of  the  embankment 
was  maintained  basin-shaped 
during  construction,  being  low- 
er at  the  axis  than  at  the  outer 
slopes  by  i-io,  to  the  height  be- 
low the  finished  crown.  This 
gave  a  grade  of  about  i  in  25 
from  the  edges  toward  the  cen- 
ter, resulting  in  the  following 
advantages : 

(1)  Insuring  a  more  thorough 
wetting  of  the  central  portion  of 
the  dam ;  any  excess  of  water  in 
this  part  would  be  readily  taken 
care    of    by    the    central    cross 
drains. 

(2)  In   wetting    the    finished 
surface    prior    to    depositing  a 
new    layer    of  material,    water 
from     the     sprinkling     wagons 
would  naturally   drain  towards 
the  center  and  insure  keeping 
the  surface  wet;  the  layers  be- 
ing carried,  as  a  rule,  progres- 
sively outward  from  the  center. 

(3)  It   centralized   the   maxi- 
mum   earth    pressure    and    en- 
abled the  depositing  of  material 
in  layers  perpendicular   to   the 
slopes. 

(4)  It  facilitated   rolling  and 
hauling  on  lines  parallel  to  the 
axis  of  the  dam,  and  discour- 
aged transverse  and  miscellane- 
ous operations. 

(5)  It   finally   insured   better 
compacting  by  the  tramping  of 
teams  in  their  exertions  to  over- 
come the  grade. 

The   specifications    stipulated 
that  the  body  of  the  dam  should 


\ 


THE  TABEAUD  DAM. 


28  EARTH  DAMS. 

be  built  up  in  layers  not  exceeding  6  ins.  in  thickness  for  the  first 
60  ft.,  and  not  exceeding  8  ins.  above  that  elevation.  The  finished 
layers  after  rolling  varied  slightly  in  thickness,  the  daily  average 
per  month  being  as  follows : 

April 4  ins.  August 5  ins. 

May 3^2"  September    6    ' 

June 4     "  October 7    ' 

July 4/^j"  November  and  December.  .  8 

During  the  last  few  months  more  than  one  whole  layer  consti- 
tuted the  day's  work,  so  that  a  single  layer  was  seldom  as  thick 
as  the  daily  average  indicates. 

It  was  stipulated  in  the  specifications  that  the  up-stream  half 
of  the  dam  was  to  be  made  of  "selected  material"  and  the  lower 
half  of  less  choice  material,  not  designated  "waste."  "Waste  ma- 
terial" was  described  as  meaning  all  vegetable  humus,  light  soil, 
roots,  and  rock  exceeding  5  Ibs.  in  weight,  too  large  to  pass 
through  a  4-in.  ring. 

It  may  be  well  to  define  the  expression  "selected  material,"  so 
commonly  used  in  specifications  for  earth  dams.  In  England,  for 
instance,  it  is  said  to  refer  to  materials  which  insure  water-tight- 
ness, while  in  India  it  refers  to  those  employed  to  obtain  stability. 
•  •It  ought  to  mean  the  best  material  available,  selected  by  the  engi- 
neer to  suit  the  requirements  of  the  situation. 

The  method  employed  in  building  the  body  of  the  embankment 
may  be  described  as  follows : 

(1)  The  top  surface  of  every  finished    layer    of    material    was 
sprinkled  and  harrowed  prior  to  putting  on    a    new    layer.     The 
sprinkling  wagons  passed  over  the  older  finished  surface  imme- 
diately  before   each   wagon-row    was    begun.       This    insured    a 
wetted  surface  and  assisted  the  wheels  of  the  loaded  wagons,  as 
we'll  as  the  harrows,  to  roughen  the  old  surface  prior  to  deposit- 
ing a  new  layer. 

(2)  The  material  was   generally  deposited  in   rows   parallel  to 
the  axis  of  the  dam.     However,  along  the  line  of  contact,  at  the 
margins  of  the  embankment,  the  earth  was   often    deposited    in 
rows  crosswise  of  the  dam,  permitting  a  selection  of  the  choicest 
materials  and  greatly  facilitating  the  work  of  graders  and  rollers. 

(3)  Rock  pickers  with  their  carts  were  continually  passing  along 
the  rows  gathering  up  all  roots,  rocks  and  other  waste  materials. 

(4)  The  road-graders  drawrn  by  six  horses  leveled  down  the  tops 
of  the  wagon-loads,  and  if  the  material   was  dry  the  sprinkling 


THE  TAB  BAUD  DAM. 


29 


30  EARTH  DAMS. 

wagons  immediately  passed  over  the  rows  prior  to  further  grad- 
ing. When  the  material  was  naturally  moist  the  grader  continued 
the  leveling  process  until  the  earth  was  evenly  spread.  The  depth 
or  thickness  of  the  layer  could  be  regulated  to  a  nicety  by  prop- 
erly spacing  the  rows  and  the  individual  loads.  The  grader  brought 
the  layer  to  a  smooth  surface  and  of  uniform  thickness,  and  noth- 
ing more  could  be  desired  for  this  operation. 

(5)  After  the  graders  had  finished,  the  harrows  passed  over  the 
new  layer  to  insure  the  picking  out  of  all  roots    and   rocks,    fol- 
lowed immediately  by  the  sprinkling  wagons. 

(6)  Finally  the  rollers  thoroughly  compacted  the  layer  of  earth, 
generally  passing  to  and  fro  over  it  lengthwise  of  the  dam.    Along 
the  line  of  contact  at  the  ends,  however,  they  passed  crosswise. 
Then  again  they  frequently  went  around  a  portion  of  the  surface 
until  the  whole  was  hard  and  solid. 

Two  rollers  were  in  use  constantly,  each  drawn  by  six  horses. 
One  weighed  five  tons  and  the  other  eight  tons,  giving  respectively 
166  and  200  Ibs.  pressure  per  lin.  in.  They  were  not  grooved,  but 
the  smooth  surface  left  by  the  rollers  was  always  harrowed  and  cut 
up  more  or  less  by  the  loaded  wagons  passing  over  the  surface  pre- 
viously wetted.  The  wagons  when  loaded  gave  750  Ibs.  pressure 
per  lin.  in.,  and  the  heavy  teams  traveling  wherever  they  could  do 
the  most  effective  work  compacted  the  materials  better  even  than 
the  rollers. 

Several  test  pits  which  were  dug  into  the  dam  during  construc- 
tion showed  that  there  were  no  distinct  lines  traceable  between 
the  layers  and  no  loose  or  dry  spots,  but  that  the  whole  mass  was 
solid  and  homogeneous. 

A  careful  record  is  being  kept  of  the  amount  of  settlement  of 
the  Tabeaud  Dam.  It  will  be  of  interest  to  record  here  the  fact 
that  just  one  year  after  date  of  completion  the  settlement 
amounted  to  0.2  ft.,  with  90  ft.  depth  of  water  in  the  reservoir. 

Water  was  first  turned  into  the  reservoir  five  months  after  the 
dam  was  finished.  The  very  small  amount  of  settlement  here 
shown  emphasizes  more  eloquently  than  words  the  author's  con- 
cluding remarks  relating  to  the  importance  of  thorough  consolida- 
tion, by  artificial  means,  of  the  embankment.  (See  p.  64,  Sees. 
6  to  8.) 

OUTLET  TUNNEL. — The  outlet  for  the  reservoir  is  a  tun- 
nel 2,903  ft.  in  length,  through  a  ridge  of  solid  slate  rock  forma- 
tion, which  was  very  hard  and  refractory.  At  the  north  or  res- 


THE  TABEAUD  DAM.  31 

ervoir  end  of  the  tunnel,  there  is  an  open  cut  350  ft.  long,  with  a 
maximum  depth  of  26  ft. 

Near  the  south  portal  of  the  tunnel  and  in  the  line  of  pressure 
pipes  connecting  the  "petty  reservoir"  above  with  the  power- 
house below,  is  placed  a  receiver,  connected  with  the  tunnel  by 
means  of  a  short  pipe-line,  60  ins.  in  diameter. 

A  water-tight  bulkhead  of  brick  and  concrete  masonry  is  placed 
in  the  tunnel,  at  a  point  about  175  ft.  distant  from  the  receiver. 
In  the  line  of  6o-in,  riveted  steel  pipe,  which  connects  the  reser- 
voir and  tunnel  with  the  receiver,  there  is  placed  a  cast  iron  cham- 
ber for  entrapping  silt  or  sand,  with  a  branch  pipe  16  ins.  in  diam- 
eter leading  into  a  side  ravine  through  which  sand  or  silt  thus 
collected  can  be  wasted  or  washed  out.  By  the  design  of  construc- 
tion thus  described,  it  will  be  seen  that  all  controlling  devices, 
screens,  gates,  etc.,  are  at  the  south  end  of  the  tunnel  and  easily 
accessible. 

WASTEWAY. — The  wasteway  for  the  reservoir  is  an  open  cut 
through  its  rim,  48  ft.  in  width  and  300  ft.  long.  The  sill  of  the 
spillway  is  10  ft.  below  the  crown  of  the  dam.  The  reservoir  hav- 
ing less  than  two  square  miles  of  catchment  area,  and  the  feeding 
canals  being  under  complete  control,  the  dam  can  never  be  over- 
topped by  a  flood.  Fig.  3  shows  the  relative  location  of  the  dam^ 
outlet  tunnel  and  wasteway  channel. 

Almost  the  whole  of  the  embankment  forming  the  Tabeaud 
Dam,  not  included  in  the  foundation  work,  was  built  in  less  than 
eight  months.  The  contractor's  outfit  was  the  best  for  the  pur- 
pose the  writer  has  ever  seen.  After  increasing  his  force  from 
time  to  time  he  finally  had  the  following  equipment: 

1  steam  shovel  (il/2  yds.  capacity), 
37    patent  dump  wagons, 

ii  stick- wagons  and  rock-carts, 

39  buck-scrapers  (Fresno  pattern), 

21  wheel  scrapers, 

3  road-graders, 

3  sprinkling-wagons, 

2  harrows, 

2  rollers  (5  and  8-ton), 

233  men, 

416  horses  and  mules. 

8  road  and  hillside  plows, 


32  EARTH  DAMS. 

STATISTICS.— The    following   data   relating   to    the   Tabeaud 
Dam  Reservoir  will  conclude  this  description : 

DAM. 

Length  at  crown  636  ft. 

Length  at  base  crossing  ravine 50  to  100  " 

Height  to  top  of  crown  (El.  1,258.) 120  " 

"        at  ends  above  bedrock 117  '"' 

"        at  up-stream  toe   100  " 

"        at  down-stream  toe 123  " 

Effective  head 115  " 

Width  at  crown 20  " 

Width  at  base   620  " 

Slopes,  2l/2  on  I  with  rock-fill  3  to  i. 

Excavation  for  foundations   40,000  cu.  yds. 

Refill  by  company 40,000       " 

Embankment  built  by  contractor  330,350        " 

Total  volume  of  dam 370,350       *' 

Total  weight   664,778  tons. 

Length  of  wasteway  (width) 48  ft. 

Depth  of  spillwav  sill  below  crown  10  " 

Depth  of  spillway  sill  below  ends 7  " 

Height  of  stop-planks  in  wasteway 2  '* 

Maximum  depth  of  water  in  reservoir 92  " 

Area  to  be  faced  with  stone 1,933  sq.  yds. 

RESERVOIR. 

Catchment    area  (approximate)    2  sq.  miles. 

Area  of  water  surface  36.  75  acres. 

Silt  storage  capacity  below  outlet  tunnel 1,091,470  en.  ft. 

Available  water  storage  capacity 46,612,405      " 

Elevation  of  outlet  tunnel  1,180  ft. 

"  high-water  surface  1,250  " 

"  crown  of  dam  1,258  " 

Fig.  13  is  a  view  of  the  finished  dam,  taken  immediately  after 
completion. 


CHAPTER  V. 
Different  Types  of  Earth  Dams. 

There  are  several  types  of  earth  dams,  which  may  be  Described  as 
follows : 

1.  Homogeneous    earth  dams,  either   with  or  without  a  puddle 

trench. 

2.  Earth  dams  with  a  puddle  core  or  puddle  face. 

3.  Earth  dams   with   a   core   wall  of  brick,  rubble   or   concrete 

masonry. 

4.  New  types,  composite  structures. 

5.  Rock-fill  dams  with  earth  inner  slope. 

6.  Hydraulic-fill  dams  of  earth  and  gravel. 

The  writer  proposes  to  give  an  example  of  each  type,  with,  such 
remarks  upon  their  distinctive  features  and  relative  merits  as,  he 
thinks  may  be  instructive. 

Earth    Dams    \\~\\\\    Puddle    Core   Wall   or   Face. 

YARROW  DAM.— The  Yarrow  dam  of  the  Liverpool  Water- 
Works  is  a  notable  example  of  the  second  type,  (a  section  of  which 
is  shown  in  Fig.  2?)  An  excavation  97  At.  in  depth  was  made  to 
bed  rock  through  different  strata  of  varying  thickness,  and  a 
trench  24  ft.  wide  was  cut  with  side  slopes  I  on  I  for  the  first  10 
ft.  in  depth  below  the  surface.  The  trench  was  then  carried 
down  through  sand,  gravel  and  boulders  with  sides  sloping  I  in 
12.  The  upper  surface  of  the  shale  bed  rock  was  found  to  be  soft, 
seamy  and  water-bearing.  Pumps  were  installed  to  keep  the  water 
cut  of  the  trench  while  it  was  being  cut  4  or  5  ft.  deeper  into  the 
shale.  The  lower  portion  was  then  walled  up  on  either  side  with 
brickwork  14  ins.  in  thickness,  and  the  trench  between  the  walls 
was  filled  with  concrete,  made  in  the  proportion  of  I  of  cement, 
i  of  sand  and  2  of  gravel  or  broken  stone.  By  so  doing  a  dry  bed 
was  secured  for  the  foundation  of  the  puddle  wall.  Two  lines  of 
6-in.  pipes  were  laid  on  the  bed  rock,  outside  of  the  walls,  and 
pipes  9  ins.  in  diameter  extended  vertically  above  the  top  of  the 
brickwork  some  27  ft.  These  pipes  were  filled  with  concrete,  after 
disconnecting  the  pumps.  After  refilling  the  trench  with  puddle 
to  the  original  surface,  a  puddle  wall  was  carried  up  simultan- 


34 


EARTH  DAMS. 


\ 


x.. 


DIFFERENT  TYPES  OF  EARTH  DAMS.  35 

eons  with  the  embankment,  having  a  decreasing  batter  of  I  in  12, 
which  gave  a  width  of  6  ft.  at  the  top.  This  form  of  construction 
is  very  common  in  England,  and  Figs.  14  and  15  show  two  Cali- 
fornia dams,  the  Pilarcitos  and  San  Andres,  of  the  same  general 
type. 

ASHTI  EMBANKMENT.— This  is  not  a  very  high  embank- 
ment, but  being  typical  of  modern  dams  in  British  India,  where 
the  puddle  is  generally  carried  only  to  the  top  of  the  orig- 
inal surface  of  the  ground,  and  not  up  through  the  body  of  the 
dam,  it  is  thought  worthy  of  mention.  Fig.  16  shows  a  section  of 
this  embankment,  which  is  located  in  the  Sholapur  District,  India. 

The  central  portion  of  this  dam  above  the  puddle  trench  is  made 
of  "selected  black  soil;"  then  on  either  side  is  placed  "Brown 
Soil,"  finishing  on  the  outer  slopes  with  "Murum."  Trap  rock 
decomposes  first  into  a  friable  stony  material,  known  in  India  as 
"Murum"  or  "Murham."  This  material  further  decomposes  into 


Sc-cc 

FIG.    16.— 'CROSS-SECTION    OF    ASHTI    TANK  'EMBANKMENT. 

various  argillaceous  earths,  the  most  common  being  the  "black 
cotton  soil"  mentioned  above. 

This  particular  dam  has  been  adversely  criticised  on  account  of 
the  lack  of  uniformity  in  the  character  of  the  materials  composing 
the  bank.  It  is  claimed  that  the  materials  being  of  different  den- 
sity and  weight,  unequal  settlement  will  result,  and  lines  of  sep- 
aration will  form  between  the  different  kinds  of  materials. 

Earth  materials  do  not  unite  or  combine  with  timber  or  mason- 
ry, but  there  are  no  such  distinct  lines  of  transition  and  separation 
between  different  earth  materials  themselves  as  Fig.  16  would 
seem  to  indicate. 

Puddle   Trench* 

In  the  last  three  dams  mentioned  (Figs.  14,  15,  16)  the  puddle 
trenches  are  made  with  vertical  sides  or  vertical  steps  and  offsets. 
A  wedge-shaped  trench  certainly  has  many  advantages  over  this 


36  EARTH  DAMS. 

form.  Puddle  being  plastic,  consolidates  as  the  dam  settles,  fill- 
ing the  lowest  parts  by  sliding  on  its  bed.  It  thus  has  a  tendency 
to  break  away  from  the  portion  supported  by  the  step,  and  a  fur- 
ther tendency  to  leave  the  vertical  side,  thus  forming  cracks  and 
fissures  for  water  to  enter.  The  argument  advanced  by  those 
holding  a  different  view,  namely,  that  it  is  difficult  to  dress  the 
sides  of  a  trench  to  a  steep  batter  and  to  timber  it  substantially, 
has  in  reality  little  weight  when  put  to  practical  test.  Mr.  F.  P. 
Stearns,  in  describing  the  recent  work  of  excavating  the  cut-off 
trench  of  the  North  Dike  of  the  Wachusett  reservoir,  Boston, 
said  it  was  found  to  be  both  better  and  cheaper  to  excavate  a 
trench  with  slopes  than  with  vertical  sides  protected  by  sheeting. 
He  favored  this  shape  in  case  of  pile-work  and  for  the  purpose 
also  of  wedging  materials  together. 

Mr.  Wm.  J.  McAlpine's  "Specifications  for  Earth  Dams,"  repre- 
senting the  best  practice  of  25  years  ago,  which  are  frequently 
cited,  contain  the  following  description  of  how  to  prepare  the 
up-stream  floor  of  the  dam : 

Remove  the  pervious  and  decaying  matter  by  breaking  up  the  natural  soil 
and  by  stepping  up  the  sides  of  the  ravine;  also  by  several  toothed  trenches 
across  the  bottom  and  up  the  sides. 

One  of  Mr.  McAlpine's  well  known  axioms  was,  "water  abhors 
an  angle."  The  "stepping"  and  "toothed"  trenches  above  speci- 
fied need  not  necessarily  be  made  with  vertical  planes,  but  should 
be  made  by  means  of  inclined  and  horizontal  planes.  The  writer's 
experience  and  observation  leads  him  to  think  that  all  excavations 
in  connection  with  earth  dams  requiring  a  refill  should  be  made 
YV  edge-shaped  so  that  the  pressure  of  the  superincumbent  mater- 
ials in  settling  will  wedge  the  material  tighter  and  tighter  together 
and  fill  every  cavity.  A  paper  by  Mr.  Wm.  L.  Strange,  C.  E.,  on 
"Reservoirs  with  high  Earthen  Dams  in  Western  India,"  pub- 
lished in  the  Proceedings  of  the  Institution  of  Civil  Engineers, 
Vol.  132,  (1898),  is  one  of  the  best  contributions  to  the  literature 
on  this  subject,  known  to  the  writer.  Mr.  Strange  states  that 

the  rate  of  nitration  of  a  soil  depends  upon  its  porosity,  which  governs  the 
frictional  resistance  to  flow,  and  the  slope  and  length  of  the  filamentary 
channels  along  which  the  water  may  be  considered  to  pass.  It  is  evident, 
therefore,  that  the  direct  rate  of  infiltration  in  a  homogeneous  soil  must  de- 
crease from  the  top  to  the  bottom  of  the  puddle  trench.  The  best  section 
for  a  puddle  trench  is  thus  a  wedge,  such  as  an  open  excavation  would  give. 
It  is  true  that  the  uppermost  infiltrating  filaments  when  stopped  by  the 
puddle,  will  endeavor  to  get  under  it,  but  a  depth  will  eventually  be  reached 


DIFFERENT  TYPES  OF  EARTH  DAMS.  37 

when  the  frictional  resistance  along  the  natural  passages  will  be  greater 
than  that  due  to  the  transverse  passage  of  the  puddle  trench,  and  it  is  when 
this  occurs  that  the  latter  may  be  stopped  without  danger,  as  the  filtration  to 
it  will  be  less  than  that  that  through  it.  This  depth  requires  to  be  determined 
in  each  case,  but  in  fairly  compact  Indian  soils  30  feet  will  be  a  fair  limit. 

Puddle    Wall  vs.  Puddle   Trench. 

There  is  a  diversity  of  opinion  among  engineers  in  regard  to  the 
proper  place  for  the  puddle  in  dam  construction.  Theoretically, 
the  inner  face  would  be  preferable  to  the  center,  for  the  purpose  of 
preventing  any  water  from  penetrating  the  embankment.  It  is 
well  known  that  all  materials  immersed  in  water  lose  weight  in  pro- 
portion to  the  volume  of  water  they  displace.  If  the  upper  half  of 
the  dam  becomes  saturated  it  must  necesarily  lose  both  weight  and 
stability.  Its  full  cohesive  strength  can  only  be  maintained  by  mak- 
ing it  impervious  in  some  way.  The  strength  of  an  earth  dam  de- 
ponds  upon  three  factors : 

1.  Weight. 

2.  Frictional  resistance  against  sliding. 

3.  Cohesiveness  of  its  materials. 

These  can  be  known  only  so  long  as  no  water  penetrates  the  body 
of  the  dam.  When  once  saturated  the  resultant  line  of  pressure  is 
no  longer  normal  to  the  inner  slope,  for  the  reason  that  there  is  now 
a  force  tending  to  slide  the  dam  horizontally  and  another  due  to 
the  hydrostatic  head  tending  to  lift  it  vertically.  When  the  water 
slope  is  impervious  the  horizontal  thrust  is  sustained  by  the  whole 
dam  and  not  by  the  lower  half  alone.  When  once  a  passage  is 
made  into  the  body  of  the  dam,  the  infiltration  water  will  escape 
along  the  line  of  least  resistance,  and  if  there  be  a  fissure  it  may 
become  a  cavity  and  the  cavity  a  breach. 

For  practical  reasons,  mainly  on  account  of  the  difficulty  of  main- 
taining a  puddle  face  on  the  inner  ^lope  of  a  dam,  which  would  re- 
quire a  very  flat  slope,  puddle  is  generally  placed  at  the  center  as 
a  core  wall. 

It  was  thought  possible  at  the  Tabeaud  dam  to  counteract  the 
tendency  of  the  face  puddle  to  slough  off  into  the  reservoir  by  use 
of  a  broken  stone  facing  of  riprap.  This  covering  will  protect  the 
puddle  from  the  deteriorating  effects  of  air  and  sun  whenever  the 
water  is  drawn  low  and  also  resists  the  pressure  at  the  inner  toe 
of  the  dam. 


38  EARTH  DAMS. 

Percolation   and   Infiltration. 

The  earlier  authorities  on  the  subject  of  percolation  and  infiltra- 
tion of  water  are  somewhat  conflicting  in  their  statements,  if  not 
confused  in  their  ideas.  We  are  again  impressed  with  the  import- 
ance of  a  clearly  defined  and  definite  use  of  terms.  The  temptation 
and  tendency  to  use  language  synonymously  is  very  great,  but  it  is 
unscientific  and  must  result  in  confusion  of  thought.  Let  it  be  ob- 
served that  filtration  is  the  process  of  mechanically  separating  and 
removing  the  undissolved  particles  floating  in  a  liquid.  That  in- 
filtration is  the  process  by  which  water  (or  other  liquid)  enters  the 
interstices  of  porous  material.  That  percolation  is  the  action  of  a 
liquid  passing  through  small  interstices ;  and,  finally,  that  seepage 
is  the  amount  of  fluid  which  has  percolated  through  porous  mater- 
ials. 

Many  recent  authorities  are  guilty  of  confusion  in  thought  or 
expression,  as  will  apoear  from  the  following: 

One  says,  for  instance,  that  a 

rock  is  water-tight  when  non-absorbent  of  water,  but  that  a  soil  is  not  water- 
tight unless  it  will  absorb  an  enormous  quantity  of  water. 

This  would  seem  to  indicate  that  super-saturation  and  not  pres- 
sure is  necesary  to  increase  the  water-tightness  of  earth  materials. 

Again,  in  a  recent  discussion  regarding  the  saturation  and  perco- 
lation of  water  through  the  lower  half  of  a  reservoir  embankment, 
it  was  remarked,  that 

the  more  compact  the  material  of  which  the  bank  is  built,  the  steeper  will 
be  the  slope  of  saturation. 

Exception   was   taken   to   this,   and   the   statement   made,   that 

with  compact  material,  the  sectional  area  of  flow  is  larger  below  a  given  level 
with  porous  material,  and  as  the  bank  slope  is  one  determining  factor  of  the 
line  of  saturation,  this  line  tends  to  approach  the  slope  line;  while  with  por- 
ous material  in  a  down-stream  bank,  the  slope  of  saturation  is  steeper  and 
the  area  of  the  flow  less. 

In  reply  to  this,  it  was  said, 

that  it  is  obvious  that  if  the  embankment  below  the  core  wall  is  built  of  ma- 
terial so  compact  as  to  be  impervious  to  water,  no  water  passing  through 
the  wall  will  enter  it,  and  the  slope  of  saturation  will  be  vertical.  If  it  be 
less  compact,  water  will  enter  more  or  less  according  to  the  head  or  press- 
ure, and  according  to  its  compactness  or  porosity,  producing  a  slope  of  sat- 
uration whose  inclination  is  dependent  on  the  frictional  resistance  encoun- 
tered by  the  water.  And  the  bank  will  be  tight  whenever  the  slope  of  sat- 
uration remains  within  the  figure  of  the  embankment. 


DIFFERENT  TYPES  OF  EART 


Further, 

that  it  was  necessary  to  distinguish  between  the  slope  assumed 
by  water  retained  in  an  embankment  and  that  taken  by  water  passing 
through  an  embankment  made  of  material  too  porous  to  retain  it;  where  the 
rule  is  clearly  reversed  and  where  the  more  porous  the  material  the 
steeper  the  slope  at  which  water  will  run  through  it  at  a  given  rate. 

These  citations  are  sufficient  to  emphasize  the  importance  of 
exact  definition  of  terms  and  clear  statement  of  principles. 

The  latest  experiments  relating  to  the  percolation  of  water 
through  earth  materials  and  tests  determining  the  stability  of  soils 
are  those  made  during  the  investigations  at  the  New  Croton  Dam 
and  Jerome  Park  Reservoir,  New  York,  and  those  relating  to  the 
North  Dike  of  the  Wachusett  Reservoir,  Boston.  These  are  very 
interesting  and  instructive,  and  it  is  here  proposed  to  discuss  the 
results  and  conclusions  reached  in  these  cases,  after  some  intro- 
ductory remarks  reciting  the  order  of  events. 

NEW  CROTON  DAM.— In  June,  1901,  the  Board  of  Croton 
Aqueduct  Commissioners  of  New  York  requested  a  board  of  ex- 
pert engineers,  consisting  of  Messrs.  J.  J.  R.  Croes,  E.  F.  Smith 
and  E.  Sweet,  to  examine  the  plans  for  the  construction  of  the 
earth  portion  of  the  New  Croton  Dam,  and  also  the  core  wall  and 
embankment  of  the  Jerome  Park  reservoir. 

This  report  was  published  in  full  in  Engineering  News  for  Nov. 
28,  1901.  It  was  followed  in  subsequent  issues  of  the  said  journal 
by  supplemental  and  individual  reports  from  each  member  of  the 
board  of  experts,  and  by  articles  from  Messrs.  A.  Fteley,  who  orig- 
inally designed  the  works,  A.  Craven,  formerly  division  engineer 
on  this  work,  and  W.  R.  Hill,  at  that  time  chief  engineer  of  the 
Croton  Aqueduct  Commission. 

After  describing  the  New  Croton  Dam,  the  board  of  experts  pref- 
ace their  remarks  on  the  earth  embankment  by  saying  that 
it  has  been  abundantly  proven  that  up  to  a  height  of  60  or  70  ft.  an  embank- 
ment founded  on  solid  material  and  constructed  of  well-selected  earth,  prop- 
erly put  in  place,  is  fully  as  durable  and  safe  as  a  masonry  wall  and  far*  less 
costly. 

There  are,  in  fact,  no  less  than  22  earth  dams  in  use  to-day 
exceeding  90  ft.  in  height,  and  twice  that  number  over  70  ft.  in 
height.  Five  of  the  former  are  in  California,  and  several  of  these 
have  been  in  use  over  25  years.  The  writer  fails  to  appreciate  the 
reason  for  limiting  the  safe  height  of  earth  dams  to  60  or  70  ft. 

The  New  Croton  Dam  was  designed  as  a  composite  structure  of 
masonry  and  earth,  crossing  the  Croton  Valley  at  a  point  three 


40  EARTH  DAMS. 

miles  from  the  Hudson  River.  The  earth  portion  was  to  join  the 
masonry  portion  at  a  point  where  the  latter  was  195  ft.  high  from 
the  bed  rock.  The  Board  thought  there  was  no  precedent  for  such 
a  design  and  no  necessity  for  this  form  of  construction.  The  point 
to  be  considered  here  was  whether  a  dam  like  this  can  be  made  suf- 
ficiently impermeable  to  water  to  prevent  the  outer  slope  from  be- 
coming saturated  and  thus  liable  to  slide  and  be  washed  out. 

The  design  of  the  embankment  portion  was  similar  to  all  the 
earth  dams  of  the  Croton  Valley.  In  the  center  is  built  a  wall  of 
rubble  masonry,  generally  founded  upon  solid  rock,  and  "intended 
to  prevent  the  free  seepage  of  water,  but  not  heavy  enough  to  act 
alone  as  a  retaining  wall  for  either  water  or  earth." 

Fig.  17  shows  a  section  which  is  typical  of  most  New  England 
earth  dams ;  and  Fig.  18,  the  sections  of  two  of  the  Croton  Val- 


SO.LE  iw 
FIG.    17.— CROSS-SECTION    OF   A    TYPICAL    NEW    ENGLAND   DAM. 

ley  dams,  New  York  water  supply.  These  dams  all  have  masonry 
core  walls,  illustrating  the  third  type  of  dams  given  on  page  33. 

The  board  of  experts  made  numerous  tests  by  means  of  borings 
into  the  Croton  Valley  dams  to  determine  the  slope  of  saturation. 
The  hydraulic  laboratory  of  Cornell  University  also  made  tests  of 
the  permeability  of  several  samples  of  materials  taken  from  pits. 
All  the  materials  examined  were  found  to  be  permeable  and  when 
exposed  to  water  to  disintegrate  and  assume  a  flat  slope,  the  sur- 
face of  which  was  described  as  "slimy." 

Pipe  wells  were  driven  at  different  places  into  the  dams  and  the 
line  of  saturation  was  determined  by  noting  the  elevations  at  which 
the  water  stood  in  them.  In  all  the  dams  the  entire  bank  on  the 
water  side  of  the  core  wall  appeared  to  be  completely  saturated. 
Water  was  also  found  to  be  standing  in  the  embankment  on  the 
down-stream  side  of  the  core  wall.  The  extent  of  saturation  of  the 
outer  bank  varied  greatly,  due  to  the  difference  in  materials,  the 


DIFFERENT  TYPES  OF  EARTH  DAMS. 


care  taken  in  building  them,  and  their  ages.  Fig.  19  gives  the  aver- 
age slopes  of  saturation  as  determined  by  these  borings. 

The  experts  stated 

that  the  slope  of  the  surface  of  the  saturation  in  the  bank  is  determined  by 
the  solidity  of  the  embankment:  The  more  compact  the  material  of  which 
the  bank  is  built,  the  steeper  will  be  the  slope  of  saturation. 

As  a  result  of  their  in- 
vestigations, the  experts 
were  of  the  opinion  that 
the  slope  of  saturation  in 
the  best  embankments 
made  of  the  material  found 
in  the  Croton  Valley  is 
about  35  ft.  per  100  ft.,  and 
that  with  materials  less 
carefully  selected  and 
placed  the  slope  may  be 
20  ft.  per  loo  ft. 

Further,  that  taking  the 
loss    of    head    in    passing 
through  the  core  wall,  and 
the  slope  assumed  by  the 
plane    of    saturation,    the 
maximum  safe  height  of  an 
earth  dam  with  its  top  20  ft.  above  wa- 
ter level  in  the  reservoir  and  its  outside 
slope  2  on  i,  is  63  to  102.5  ft.     This  is  a  re- 
markable finding  in  view  of  the  fact  that 
the  Titicus  Dam,  one  of  the  Croton  Valley 
dams   examined,  has   a  maximum   height 
above  bed  rock  of  no  ft.  and  has  been  in 
use  seven  years.    This  dam  is  not  a  fair  ex- 
ample to  cite  in  proof  of  their  conclusion, 
because   its   effective   head   is    only   about 
46  ft.* 

Mr.    Fteley     gave     as     a     reason     for 
the       elevation      of      the      water      slope 

*The  effective  head  at  any  point  of  an  earth  dam,  has 
been  defined  as  the  difference  in  elevation  of  high  water 
surface  in  the  reservoir  and  that  of  the  intersection  of 
the  down-stream  slope  with  the  natural  or  restored  sur- 
face of  the  ground  below  the  dam. 


42  EARTH  DAMS. 

found  in  the  outer  bank  of  the  Croton  dams  the  fact  of  their  being 
constructed  of  fine  materials  and  stated  that  with  comparatively 
Dorous  materials  they  would  have  shown  steeper  slopes  of  satura- 
tion. 

Mr.  Craven  argued  that  all  dams  will  absorb  more  or  less  water, 
and  that  porosity  is  merely  a  degree  of  compactness ;  that  slope  im- 
plies motion  in  water,  and  that  there  is  no  absolute  retention  of 
water  in  the  outer  bank  of  a  dam  having  its  base  below  the  plane 
indicated  by  the  loss  of  head  in  passing  through  the  inner  bank 
and  then  through  a  further  obstruction  of  either  masonry  or  pud- 
die;  that  there  is  simply  a  partial  retention,  with  motion  through 
the  bank  governed  by  the  degree  of  porosity  of  the  material. 

Fig.  19  is  a  graphical  interpretation  of  the  conclusion  reached 
by  the  board  of  experts,  as  already  given  on  page  41.  "A"  is  an 
ideal  profile  of  a  homogeneous  dam  with  the  inner  slope  3  on  I  and 
the  outer  slope  2  on  I.  The  top  width  is  made  25  ft.  for  a  dam  hav- 
ing 90  ft.  effective  head,  the  high  water  surface  in  the  reservoir 
being  10  ft.  below  the  crest  of  the  dam.  This  ideal  profile  is  a 
fair  average  of  all  the  earth  dams  of  the  world.  Not  having  a  core 
wall  to  augment  the  loss  of  head,  it  fairly  represents  what  might 
be  expected  of  such  a  dam  built  of  Croton  Valley  material,  com- 
pacted in  the  usual  way.  It  should  be  noted  that  the  intersection 
of  the  plane  of  saturation  with  the  rear  slope  of  the  dam  at  such 
high  elevation  as  shown  indicates  an  excessive  seepage  and  a  dan- 
gerously unstable  condition. 

Preliminary   Study   of   Profile   for   Dam. 

The  preliminary  calculations  for  desiging  a  profile  for  an  earth 
dam  are  simple  and  will  here  be  illustrated  by  an  example.  Let 
us  assume  the  following  values : 

a.  Central  height  of  dam,  100  ft. 

b.  Maximum  depth  of  water,  90  ft.,  with  surface   10  ft.  below 
crest  of  dam. 

c.  Effective  head,  90  ft. 

d.  Weight  of  water,  62.5  Ibs.  per  cu.  ft. 

e.  Weight  of  material,  125  Ibs.  per  cu.  ft. 

f.  Coefficient  of  friction,  i.oo,  or  equal  to  the  weight. 

g.  Factor  of  safety  against  sliding,  10. 

The  width  corresponding  to  the  vertical  pressure  of  I  ft.  is, 
62.5  x  10 

-=5  ft. 
125 


DIFFERENT  TYPES  OF  EARTH  DAMS. 


43 


44  EARTH  DAMS. 

The  hydrostatic  pressure  per  square  foot  at  90  ft.  depth  is,  62.5  x 
90=5,625  Ibs. 

The  dam,  having  a  factor  of  safety  of  10,  must  present  a  resist- 
ance of,  5,625  x  10=56,250  Ibs.,  or  28  tons  per  square  foot. 

The  theoretical  width  of  bank  corresponding  to  90  ft.  head  and  a 
factor  of  10  is  shown  by  the  dotted  triangle  (A-B-B)  to  be  450  ft., 
(B,  Fig.  19)  with  slopes  2.\  on  i. 

To  this  must  be  added  the  width  due  to  the  height  of  crest  above 
the  water  surface  in  the  reservoir  and  the  width  of  crest. 

The  former  would  be,  2  (2^  x  io)=5o  ft.,  and  the  latter  by  Traut- 
v/ine's  rule,  2  +  2^100=22  ft.,  giving  a  total  base  width  of  522  ft. 

Let  us  now  assume  that  the  slope  of  saturation  may  be  35  ft.  per 
100  ft.  We  observe  that  this  intersects  the  base  40  ft.  within  the 
outer  toe  of  the  bank  slope.  If  the  plane  of  saturation  was  33  ft. 
per  100,  it  would  just  reach  the  outer  toe.  It  would  be  advisable 
to  enlarge  this  section  by  adding  a  lo-ft.  berm  at  the  5o-ft.level, 
having  a  slope  not  less  than  3  on  i  for  the  up-stream  face,  and  two 
I5~ft.  berms  on  the  down-stream  face,  having  slopes  2^  on  I.  The 
additional  width  of  base  due  to  these  modifications  in  our  profile 
amounts  to  65  ft.,  giving  a  total  base  width  of  587  ft.,  and  increas- 
ing the  factor  of  safety  from  10  to  13.  It  should  be  remembered 
that  if  the  bank  becomes  saturated  this  factor  of  safety  may  be  re- 
duced $0%,  the  coefficient  of  moist  clay  being  0.50. 

The  loss  of  head  due  to  a  core  wall  of  masonry,  as  designed  for 
the  New  Croton  Dam,  was  assumed  by  the  board  of  experts  to  be  21 
ft.,  or  17%  of  the  depth  of  water  in  full  reservoir.  It  has  been 
stated  by  several  authorities  that  the  primary  object  of  a  masonry 
core  wall  is  to  afford  a  water-tight  cut-off  to  any  water  of  perco- 
lation which  may  reach  it  through  the  upper  half  of  the  embank- 
ment. It  appears  that  absolute  water-tightness  in  the  core  wall 
is  not  obtained,  although  the  core  walls  of  the  Croton  dams  are  said 
to  be  "the  very  best  quality  of  rubble  masonry  that  can  be  made." 

Mr.  W.  W.  Follett,  who  is  reported  to  have  had  considerable  ex- 
perience in  building  earth  dams,  and  who  has  made  some  valuable 
suggestions  thereupon,  is  emphatic  in  saying, 

that  the  junction  of  earth  and  masonry  forms  a  weak  point,  that  either  a 
puddle  or  masonry  core  in  an  earthen  dam  is  an  element  of  weakness  rather 
than  strength. 

He  also  thinks  the  usual  manner  of  segregating  and  depositing 
materials  different  in  density  and  weight,  and  thus  subject  to  differ- 


DIFFERENT  TYPES  OF  EARTH  DAMS.  45 

ent  amounts  of  settlement,  as  bad  a  form  of  construction  as  could 
be  devised. 

Core  walls  may  prevent  "free  passage  of  water"  and  "excessive 
seepage,"  but  are  nevertheless  of  doubtful  expediency. 

Earthwork   Slips   and   Drainage. 

Mr.  John  Newman,  in  his  admirable  treatise  on  "Earthwork  Slips 
and  Subsidences  upon  Public  Works,"  classifies  and  enumerates 
slips  as  follows : 

Natural  causes,  7. 

Artificial  causes,  31. 

Additional  causes  due  to  impounded  water,  7. 

After  describing  each  cause  he  presents  39  different  means  used 
to  prevent  such  slips  and  describes  methods  of  making  repairs. 

Mr.  Wm.  L.  Strange  has  had  such  a  large  and  valuable  experi- 
ence and  has  set  forth  so  carefully  and  lucidly  both  the  principles 
and  practice  of  earth  dam  construction,  that  the  writer  takes  pleas- 
ure in  again  quoting  him  on  the  subject  of  drainage,  of  which  he  is 
an  ardent  advocate.  He  says  that, 

thorough  drainage  of  the  base  of  a  dam  is  a  matter  of  vital  necessity,  for 
notwithstanding  all  precautions,  some  water  will  certainly  pass  through  the 
puddle. 

It  is  at  the  junction  of  the  dam  with  the  ground  that  the  maxi- 
mum amount  of  leakage  may  be  expected.  The  percolating  water 
should  be  gotten  out  as  quickly  as  possible.  The  whole  method  of 
dealing  with  slips  may  be  summed  up  in  one  word — drainage. 

The  proper  presentation  of  these  two  phases  of  our  subject  would 
in  itself  require  a  volume.  The  interested  reader  is  therefore  re- 
ferred to  the  different  authorities  and  writers  cited  in  Appendix  II. 

Jerome   Park    Reservoir   Embankments* 

The  Jerome  Park  reservoir  is  an  artificial  basin  involving  the  ex- 
cavation and  removal  of  large  quantities  of  soil,  and  the  erection  of 
long  embankments  with  masonry  core  walls,  partly  founded  on 
rock  and  partly  on  sand.  The  plan  and  specifications  call  for  an 
embankment  20  ft.  wide  on  top,  with  both  slopes  2  on  I,  and  pro- 
vide for  lining  the  inner  slope  with  brick  or  stone  laid  in  concrete, 
and  for  covering  the  bottom  with  concrete  laid  on  good  earth  com- 
pacted by  rolling. 


46 


EARTH  DAMS. 


DIFFERENT  TYPES  OF  EARTH  DAMS.  47 

Wherever  bed  rock  was  not  considered  too  deep  below  the  sur- 
face the  core  walls  were  built  upon  it.  In  other  places  the  founda- 
tion was  placed  8  to  10  ft.  below  the  bottom  of  the  reservoir  and 
rested  upon  the  sand. 

It  appears  that  the  plans  of  the  Jerome  Park  embankment  were 
changed  from  their  original  design,  prior  to  the  report  of  the  board 
of  experts,  on  account  of  two  alleged  defects,  namely,  "cracks  in 
the  core  wall"  and  "foundation  of  quicksand,"  and  incidentally  on 
account  of  the  supposed  instability  of  the  inner  bank. 

In  describing  the  materials  on  which  these  embankments  rest 
the  experts  remarked 

that  all  these  fine  sands  are  unstable  when  mechanically  agitated  in  an  ex- 
cess of  water,  and  that  they  all  settle  in  a  firm  and  compact  mass  under  the 
water  when  the  agitation  ceases.  That  they  are  quite  unlike  the  true  quick- 
sands whose  particles  are  of  impalpable  fineness  and  which  are  "quick"  or 
unstable  under  water. 

Fig.  20  is  a  graphic  exhibit  of  the  results  of  tests  made  at  "Sta- 
tion 76  +  20,"  and  at  "Station  99,"  to  determine  the  flow  line  of 
water  in  the  sand  strata  underlying  the  embankment  and  bottom  of 
the  Jerome  Park  reservoir. 

The  experts  reported  that  there  was  no  possible  danger  of  slid- 
ing or  sloughing  of  the  bank ;  that  the  utmost  that  could  be  expect- 
ed would  be  the  percolation  of  a  small  amount  of  water  through  the 
embankment  and  the  earth ;  and  that  this  would  be  carried  off  by 
the  sewers  in  the  adjacent  avenues ;  that  a  large  expenditure  to 
prevent  such  seepage  would  not  be  warranted  nor  advisable. 

In  concluding  their  report,  however,  they  recommended  chang- 
ing the  inner  slope  of  2  on  i  to  2j  on  I,  and  doubling  the  thickness 
of  the  concrete  lining  at  the  foot  of  the  slope  to  preclude  all 
possibility  of  the  sliding  or  the  slipping  of  the  inner  bank  in  case  of 
the  water  being  lowered  rapidly  in  the  reservoir. 

Mr.  W.  R.  Hill,  then  chief  engineer  of  the  Croton  Aqueduct 
Commission,  favored  extending  the  core  walls  to  solid  rock.  He 
took  exception  to  the  manner  of  obtaining  samples  of  sand  by 
means  of  pipe  and  force-jet  of  water,  claiming  that  only  the  coarsest 
sand  was  obtained  for  examination.  He  did  not  consider 
fine  sand  through  which  three  men  could  run  a  f-in.  rod  19  and  20 
ft.  to  rock  without  use  of  a  hammer,  very  stable  material  upon 
which  to  build  a  wall. 


48  EARTH  DAMS. 

North   Dike   of   the   Wachnsett   Reservoir,    Boston. 

The  North  Dike  of  the  Wachusett  Reservoir  is  another  large  pub- 
lic work  in  progress  at  the  present  time.  It  is  of  somewhat  unusual 
design  and  the  preliminary  investigations  and  experiments  which 
led  to  its  adoption  are  interesting  in  the  extreme.* 

The  area  to  be  explored  in  determining  the  best  location  for  the 
dike  was  great,  and  the  preliminary  investigations  conducted  by 
means  of  wash  drill  borings,  very  extensive.  A  total  of  1,131  bor- 
ings were  made  to  an  average  depth  of  83  ft.,  the  maximum  depth 
being  286  ft.  The  materials  were  classified  largely  by  the  appear- 
ance of  the  samples,  though  chemical  and  filtration  tests  were  also 
made.  The  plane  of  the  ground  water  was  from  35  to  50  ft.  below 
the  surface,  and  the  action  of  the  water-jet  indicated  in  a  measure 
the  degree  of  permeability  of  the  strata. 

In  addition  to  these  tests  experimental  dikes  of  different  mater- 
ials, and  deposited  in  different  ways,  were  made  in  a  wooden  tank 
6  ft.  wide,  8  ft.  high  and  60  ft.  long.  The  stability  of  soils  when  in 
contact  with  water  was  experimented  with,  as  shown  in  Fig.  21,  in 
the  following  manner : 

An  embankment  (Fig.  21)  was  constructed  in  the  tank  of  the  ma- 
terial to  be  experimented  with,  2  ft.  wide  on  top,  6  ft.  high,  with 
slopes  2  on  i,  and  water  admitted  on  both  sides  to  a  depth  of  5  ft. 
The  top  was  covered  with  4-in.  planks  2  ft.  long  and  pressure  ap- 
plied by  means  of  two  jack  screws  resting  upon  a  cross  beam  on 
top  of  the  planks. 

With  a  pressure  of  three  tons  per  square  foot,  the  4-in. planks 
were  forced  down  into  the  embankment  a  little  more  than  6  ins., 
resulting  in  a  very  slight  bulging  of  the  slopes  a  little  below  the 
water  level.  Immediately  under  the  planks  the  soil  became  hard 
and  compact.  A  man's  weight  pushed  a  sharp  steel  rod,  f-in.  in 
diameter,  only  6  to  8  ins.  into  the  embankment  where  the  pressure 
was  applied,  while  outside  of  this  area  the  rod  was  easily  pushed  to 
the  bottom  of  the  tank. 

These  results  corroborate  in  a  general  way  the  practical  experi- 
ence of  the  author,  both  in  compressed  embankments,  where  he 
found  it  necessary  to  use  a  pick  vigorously  to  loosen  the  material 
of  which  they  were  composed,  and  in  embankments  made  by  mere- 

*This  work  is  very  fully  described  in  the  Annual  Reports  of  the  Metropolitan  Water 
Board  of  Boston:  and  by  Mr.  F.  P.  Stearns,  Chief  Engineer  of  the  'Metropolitan  Water 
and  Sewerage  Board,  in  the  Proceedings  of  the  American  Society  of  Civil  Engineers 
for  April,  1902.  The  latter  description  was  reprinted,  with  the  omission  of  some  of 
the  illustrations,  in  Engineering  News  for  May,  8,  1902. 


DIFFERENT  TYPES  OF  EARTH  DAMS 


50  EARTH  DAMS. 

]y  dumping  the  material  from  a  track,  in  which  case  the  earth  is  so 
slightly  compressed  that  an  excavation  is  easily  made  with  a  shovel. 

The  difference  in  the  coefficient  of  friction  of  the  same  material 
when  dry  and  when  wet  greatly  modifies  the  form  of  slope.  The 
harder  and  looser  the  particles,  the  straighter  will  be  the  slope  line 
in  excavation  and  slips.  The  greater  the  cohesion  of  the  earth,  the 
more  curved  will  be  the  slope,  assuming  a  parabolic  curve  near  the 
top — the  true  form  of  equilibrium. 

RATE  OF  FILTRATION.— The  rate  of  filtration  through  dif- 
ferent soils  was  experimented  with  by  forming  a  dike  in  the  tank 
previously  mentioned,  as  shown  in  Fig.  22. 

The  dike  was  made  full  8  ft.  high,  7  ft.  wide  on  top,  with  a  slope 
on  the  up-stream  side  of  2  on  I,  and  on  the  down-stream  side  4 
on  i.  This  gave  a  base  width  of  55  ft.  Immediately  over  the  top 
of  the  dike  there  was  placed  3  ft.  of  soil  to  slightly  consolidate  the 
top  of  the  bank  and  permit  the  filling  of  the  tank  to  the  top  without 
overflowing  the  dike.  The  water  pressure  in  different  parts  of  the 
dike  was  determined  by  placing  horizontal  pipes  through  the  soil 
cross-wise  of  the  tank.  These  pipes  were  perforated  and  covered 
with  wire  gauze,  being  connected  to  vertical  glass  tubes  at  their 
ends.  The  end  of  the  slope  on  the  down-stream  side  terminated 
in  a  box  having  perforated  sides  and  filled  with  gravel,  thus  en- 
abling the  water  to  percolate  and  filter  out  of  the  bank  without  car- 
rying the  soil  with  it. 

When  the  soil  was  shoveled  loosely  into  the  tank,  without  con- 
solidation of  any  kind,  it  settled  on  becoming  saturated  and  became 
quite  compact.  It  took  five  days  for  the  water  to  appear  in  the 
sixth  gage  pipe  near  the  lower  end  of  the  tank.  After  the  pressure, 
which  was  maintained  constant,  had  been  on  for  several  weeks, 
the  seepage  amounted  to  one  gallon  in  22  minutes.  When  the  soil 
was  deposited  by  shoveling  into  the  water,  the  seepage  amounted 
!  to  one  gallon  in  34  minutes. 

The  relative  filtering  capacities  of  soils  and  sands  were  thought 
to  be  better  determined  by  the  use  of  galvanized  iron  cylinders  of 
known  areas. 

Fig.  23  shows  one  of  the  cylinders.  These  latter  experiments 
confirmed  those  previously  made  at  Lawrence,  by  Mr.  Allen  Hazen, 
lor  the  Massachusetts  State  Board  of  Health.  They  showed  that 
the  loss  of  head  was  directly  proportioned  to  the  quantity  of  water 


Material, 
(i)     Soil                      

Unit  ratios. 
i 

(2)     Very  fine  sand 

14. 

(3)     Fine   sand        .    .          

176 

(4)     Medium  sand  

784 

CO     Coarse  sand  . 

4.3=^ 

DIFFERENT  TYPES  OF  EARTH  DAMS.  51 

filtered  and  that  the  quantity  filtered  will  vary  as  the  square  of  the 
diameter  of  the  effective  size  of  the  grains  of  the  filtering  material.* 
The  material  classed  as  "permeable"  at  the  North  Dike  of  the 
Wachusett  Reservoir  has  an  effective  diameter  of  about  0.20  mm. 
A  few  results  are  given  in  the  following  table : 

Amount  of  Filtration  in  Gallons  per  Day,  Through  an  Area  of  10,000  Sq.  Ft, 
With  a  Loss  of  Head  or  Slope  of  i  ft.  in  10  ft. 

U.  S.  gallons. 

7,200 
90,000 
400,000 
2,200,000 

To  be  sure  that  the  accumulation  of  air  in  the  small  interstices 
of  the  soil  was  not  the  cause  of  the  greatly  reduced  filtration  through 
it,  another  series  of  experiments  was  conducted  in  the  wooden  tank, 
as  shown  in  Fig.  24. 

A  pair  of  screens  was  placed  near  each  end  of  the  tank,  filled 
with  porous  material,  sand  and  gravel,  and  the  5o-ft.  space  between 
filled  with  soil.  The  soil  was  rammed  in  3-in.  layers,  and  special 
care  taken  to  prevent  water  from  following  along  the  sides  and 
bottom  of  the  tank.  One  end  was  filled  with  water  to  near  the  top, 
while  the  other  end  gave  a  free  outlet. 

After  this  experiment  had  been  continued  for  more  than  a  month, 
the  amount  of  seepage  averaged  1.7  gallons  per  24  hours,  or  about 
32  drops  per  minute. 

Filtration  tests  were  also  made  through  soil  under  150  ft.  head, 
0^5  Ibs.  per  sq.  in.,  with  results  not  materially  different,  it  is  stated, 
from  those  already  given.  The  soil  used  in  all  these  tests  con- 
tained from  4  to  8%  by  weight  of  organic  matter.  This  was  burned 
and  similar  tests  made  with  the  incinerated  soil,  resulting  in  an  in- 
crease of  about  20%  more  seepage  water. 

PERMANENCE  OF  SOILS.— This  last  material  experimented 
with  suggests  the  subject  of  permanence  of  soils.  This  was  report- 
ed upon  separately  and  independently  by  Mr.  Allen  Hazen  and 
Prof.  W.  O.  Crosby.  These  experts  agreed  in  their  conclusion, 
stating 

that  the  process  of  oxidation  below  the  line  of  saturation  would  be   ex- 
tremely slow,  requiring  many  thousands  of  years  for  the  complete  removal 

*By  effective  size  of  sand  grains  is  meant  such  size  of  grain  that  10%  by  weight  ol 
the  particles  are  smaller,  and  90%  larger  than  itself;  or,  to  express  it  a  little  differently, 
the  effective  size  is  equal  to  a  sphere  the  volume  of  which  is  greater  than  Vio  that 
forming  the  weight  and  is  less  than  Vio  that  forming  the  weight. 


52  EARTH  DAMS. 

of  all  the  organic  matter,  and  that  the  tightness  of  the  bank  would  not  be 
materially  affected  by  any  changes  which  are  likely  to  occur. 

It  has  been  remarked, 

that  of  all  the  materials  used  in  the  construction  of  dams,  earth  is  physically 
the  least  destructible  of  any.  The  other  materials  are  all  subject  to  more 
or  less  disintegration,  or  change  in  one  form  or  another,  and  in  earth  they 
reach  their  ultimate  and  most  lasting  form. 

In  speaking  of  the  North  Dike  of  the  Wachusett  Reservoir,  Mr. 
Stearns  remarked  that, 

it  was  evident  by  the  application  of  Mr.  Hazen's  formula  for  the  flow  of 
water  through  sands  and  gravels,  that  the  very  fine  sands  found  at  a  con- 
siderable depth  below  the  surface  would  not  permit  enough  water  to  pass 
through  them  if  a  dike  of  great  width  were  constructed,  to  cause  a'  serious 
loss  of  water,  and  it  was  also  found  that  the  soil,  which  contained  not  only 
the  fine  particles  or  organic  matter,  but  also  a  very  considerable  amount  of 
fine  comminuted  particles,  which  the  geologist  has  termed  "rock  flour," 
would  be  sufficiently  impermeable  to  be  used  as  a  substitute  for  clay  puddle. 

Fig.  25  shows  the  maximum  section  of  the  North  Dike  with  its 
cut-off  trench.  The  quantities  and  estimated  cost  of  the  completed 
structure  are  given  in  the  table  herewith : 


Work.                                Quantities.          I 
Soil  .                                       5  250  ooo  cu  yds 

Jnit  price. 

Actual. 
$262  500 

"•>           1 
Per  cent, 
total. 

Id  7 

Cut-off  trench   542  ooo       " 

20 

108  400 

10  ^ 

Borrowed  earth  and  gravel    200,000       " 
Slope  paving   50  ooo       " 

.20 
2  2O 

40,000 
no  ooo 

146 

Sheet-piling,  pumping,   etc  

117  ooo 

TC    C 

Engineering  and  preliminary  investigations  / 

A3*.... 

120,000 

15-9 

Total  cost $757,900         loo.o 

Druid   Lake   Dam,    Baltimore,   vi«l. 

Another  very  interesting  and  instructive  example  of  high  earth 
dam  construction  is  that  of  the  Druid  Lake  Reservoir  embankment, 
Baltimore,  Md. 

This  dam  was  built  under  the  supervision  of  Mr.  Robt.  K.  Mar- 
tin. Construction  was  begun  in  1864,  and  the  dam  was  finished  in 
1870.  Mr.  Alfred  M.  Quick,  present  chief  engineer  of  the  water- 
works of  the  City  of  Baltimore  has  given  a  very  lucid  description 
of  this  work  in  Engineering  News  of  Feb.  20,  1902. 

Fig.  26  is  a  cross-section  of  this  dam,  showing  the  method  of 
construction  so  clearly  as  to  scarcely  need  further  description. 
The  banks  D-D  on  either  side  of  the  central  puddle  wall  were  car- 


DIFFERENT  TYPES  OF  EARTH  DAMS. 


53 


ried  up  in  6-in.  layers  with 
horses  and  carts,  and  kept  about 
2  ft.  higher  than  the  puddle 
trench,  which  always  contained 
water.  The  banks  E-E  were 
made  of  dumped  material,  after 
which  the  basins  F-F  were  first 
filled  with  water  and  finally  filled 
by  dumping  material  into  the 
water  from  tracks  being  moved 
in  toward  the  center. 

After  reaching  the  top  of  this 
fill,  banks  B-B-B  were  built  up 
in  layers  similar  to  D-D.  The 
second  set  of  basins  C-C  were 
then  filled  in  a  manner  similar 
to  F-F.  The  remaining  portion 
A-A  was  constructed  in  layers 
like  D-D  and  B-B,  with  the  ad- 
dition of  compacting  each  layer 
with  a  heavy  roller. 

Finally  the  inner  face  slope 
was  carred  up  in  3-in.  layers  and 
thoroughly  rolled,  after  which  2 
ft.  of  "good  puddle"  was  put 
upon  the  inner  slope  the  latter 
was  rip-rapped,  the  crown  cov- 
ered with  gravel  and  the  rear 
slope  sodded. 

Some  years  after  completion, 
a  driveway  was  built  along  the 
outer  slope,  as  shown,  which 
had  a  tendency  to  strengthen 
the  dam,  though  not  designed 
expressly  for  that  purpose. 

It  is  of  interest  to  know  that 
the  influent,  effluent  and  drain 
pipes  were  originally  con- 
structed through  or  under 
the  embankment.  These  pipes 
were  laid  upon  solid  earth, 
and  where  they  passed 


54  EARTH  DAMS. 

through  the  puddle  wall  were  supported  upon  stone  piers  6  ftj 
apart.  As  might  be  expected,  they  soon  cracked  badly  and  were 
finally  abandoned,  new  ones  being  placed  in  the  original  ground  at 
the  south  side  of  the  lake.  Mr.  Quick  states  that  so  far  as  is  known 
there  has  never  been  any  evidence  of  a  leak  through  the  embank- 
ment during  these  32  years  of  service. 

New   Types   of   Dams;    lloliio,  Panama,   Canal. 

A  brief  description  will  now  be  given  of  three  different  dams 
designed  for  Bohio,  on  the  proposed  Panama  Canal.  Mr.  George 
S.  Morison's  paper  before  the  American  Society  of  Civil  Engin- 
eers, on  "The  Bohio  Dam,"  and  the  discussion  thereon,  especially 
that  by  Mr.  F.  P.  Stearns,  were  quite  fully  reported  in  Engineer- 
ing News  for  March  13  and  May  8,  1902.  In  constructing 
the  Panama  Canal  it  will  be  necessary  to  impound  the  waters  of 
the  Chagres  River,  near  Bohio,  to  maintain  the  summit  level  of 
this  canal  and  supplv  water  for  lockage. 

THE  FRENCH  DESIGN.— Fig.  27  is  an  enlarged  section  of  the 
original  design  of  the  new  French  Co.  This  design  has  no  core 
wall,  but  at  the  up-stream  toe  a  concrete  wall  was  to  be  built  across 
the  river  between  the  two  lines  of  sheet-piling.  At  the  down-stream 
toe  a  large  amount  of  riprap  was  to  be  placed  to  prevent  destruc- 
tion of  the  dam  during  construction.  In  this  case  it  would  be  nec- 
essary to  construct  a  temporary  dam  above  and  also  to  use  the  ex- 
cavation for  the  locks  as  a  flood  spillway.  This  method  would  in- 
volve considerable  risk  to  the  work,  on  account  of  the  large  volume 
of  flood  waters  it  might  be  necessary  to  take  care  of  during  con- 
struction. 

ISTHMIAN  CANAL  COMMISSION.— The  dam  proposed  by 
the  Isthmian  Canal  Commission  is  shown  by  Fig.  28.  This  was  de- 
signed to  be  an.  absolutely  water-tight  closure  of  the  geological 
valley,  by  using  a  masonry  core  wall  carried  down  to  bed  rock. 
The  maximum  depth  being  129  ft.,  it  was  planned  to  rest  the  con- 
crete" wall  on  a  series  of  pneumatic  caissons  reaching  to  rock.  The 
spaces  between  the  caissons  would  be  closed  and  made  water-tight. 
Both  slopes  of  the  earth  embankment  were  to  have  horizontal 
benches  and  be  revetted  with  loose  rock. 

MR.  MORISON'S  DESIGN.— To  appreciate  fully  the  object 
and  aim  of  the  third  design,  Fig.  29,  which  may  be  called  a  new  type, 
although  similar  in  many  respects  to  the  North  Dike  of  the  Wachu- 
sett  reservoir  already  illustrated  and  described,  it  should  be  stated 
that  the  equalized  flow  of  the  Chagres  River  is  put  at  1,000  cu.  ft. 


DIFFERENT  TYPES 'OF  EARTH  DAMS. 


55 


56  EARTH  DAMS. 

per  sec.  Of  this  quantity  it  is  estimated  that  500  cu.  ft.  would  be 
needed  for  lockage  and  200  cu.  ft.  for  evaporation.  This  leaves 
300  cu.  ft.  per  sec.  available  for  seepage  and  other  losses  or  to 
be  wasted. 

It  will  thus  be  seen  that  a  scarcity  of  water  is  not  in  this  instance 
a  condition  demanding  an  absolutely  water-tight  dam.  The  amount 
of  seepage  permissible  without  endangering  the  stability  of  the 
structure  is  the  real  point  now  to  be  discussed. 

The  third  design,  which  was  proposed  by  Mr.  Morison,  is  shown 
by  Fig.  29.  The  topography  and  configuration  of  this  dam  site  is 
not  unlike  that  of  the  San  Leandro  Dam,  California,  soon  to  be  de- 
scribed, while  the  yeneral  design  is  similar,  as  has  been  remarked, 
to  the  North  Dike  of  the  Wachusett  Reservoir. 

This  third  design  contemplates  a  compound  structure,  formed  by 
two  rock-fill  dams  situated  about  2,120  ft.  apart,  with  the  inter- 
\ening  space  filled  with  loose  rock,  earth  and  other  availible  ma- 
terial. Immediately  below  the  upper  and  higher  rock-fill  dam,  it 
is  proposed  to  place  across  the  canyon  a  puddle  wall  50  ft.  in  width, 
resting  over  two  lines  of  sheet-piling  30  ft.  apart.  This  piling 
would  probably  not  reach  farther  than  50  ft.  below  tidewater,  the 
solid  rock  floor  being  about  100  ft.  deeper. 

•  Mr.  Morison  made  use  of  Mr.  Hazen's  filtration  formula  for 
estimating  the  rate  and  quantity  of  seepage  through  the  permeable 
strata  below  the  dam.  This  formula  is : 

h       t  +  io° 

V=cd2 —    where 

1          60 

V=rate  of  flow  in  meters  per  day  through  the  whole  section, 
c— constant  varying  from  450  to  1,200,  according  to  cleanness  of 
the  sand. 
d="effective  size"  of  sand  in  mm. 

h=head  in  feet. 

1— length  or  distance  water  must  pass. 

t=temperature  of  the  water  (Fahr.) 

This  formula  should  be  used  only  when  the  effective  sizes  of  sands 
are  from  o.io  to  3.0  mm.  and  with  uniformity  coefficients  below  5.0* 

Mr.  Morison  used  the  following  values  :  C=i,ooo;  d=i.o  mm. ; 
h=9O  ft. ;  1=2,500  ft. ;  t=o,o° ;  for  the  solution  of  this  problem,  and 

*The  term  "uniformity  coefficient"  is  used  to  designate  the  ratio  of  the  size  of  the 
grain  which  has  60%  of  the  sample  finer  than  itself  to  the  size  which  has  10%  finer  than 
itself.  The  method  of  determining  the  size  of  sand  grains  and  their  uniformity  coeffi- 
cients, is  fully  explained  in  Appendix  3  of  Mr.  Hazen's  book  on  "The  Filtration  of 
Public  Water  Supplies." 


DIFFERENT  TYPES  OF  EARTH  DAMS.  57 

obtained  a  velocity  of  0.002  ft.  per  sec.  The  bed  of  sand  and  gravel 
was  assumed  to  have  a  sectional  area  of  20,000  sq.  ft.  for  2,500  ft. 
in  length.  This  gives  a  seepage  of  40  cu.  ft.  per  sec. 

It  is  believed  that  the  above  rate  of  0.002  ft.  per  sec.,  equivalent  to 
I  3-8  ins.  per  minute,  or  7  ft.  per  hour,  is  not  sufficient  to  move  any 
of  the  material.  The  velocity  of  water  percolating  through  sand 
is  found  to  vary  directly  as  the  head  and  inversely  as  the  distance. 

The  value  of  "c"  in  the  formula  is  larger  for  sands  of  niters  fav- 
orable for  flow,  and  smaller  for  compacted  materials  and  dams. 

Mr.  Morison  thought  it  might  be  nearer  the  actual  conditions 
to  assume  d=o.5o  mm. ;  c=5oo;  and  1=5,000  ft. ;  in  which  case  the 
seepage  would  only  amount  to  2.5  ft.  per  sec.  In  this  last  assumption 
the  "effective  size"  of  sand  grains  is  2^  times  that  classed  as  "per- 
meable material"  at  the  North  Dike  of  the  Wachusett  Reservoir. 

Prof.  Philipp  Forchheimer,  of  Gratz,  Austria,  recommends  the 
use  of  the  formula, 

h 

— =a  V  +  b  V  2 
1 

for  the  percolation  through  soils  between  loam  and  loamy  sand. 
Sellheim,  Masoni,  Smreker,  Krober  and  other  authorities  on  fil- 
tration use  still  other  formulas,  to  which  the  reader  and  student  is 
referred  for  further  research. 

The  writer,  having*  had  occasion  in  his  professional  practice  to 
study  quite  carefully  the  subject  of  ground  waters,  and  their  per- 
colation or  flow  through  different  classes  of  materials  and  under 
varying  conditions,  is  of  the  opinion  that  rarely  does  the  cross- 
section  of  a  stream-channel,  filled  with  sand,  gravel  and  debris,  pre- 
sent, even  approximately,  a  homogeneous  or  uniform  mass ;  and 
that  there  are,  almost  without  exception,  strata  of  material  much 
coarser  and  more  porous  than  the  general  average.  In  other 
words,  that  it  is  extremely  difficult  to  arrive  at  a  uniformity  coeffi- 
cient. It  is  unwise  to  place  much  reliance  upon  an  estimated  flow 
where  this  is  the  case.  The  formula  may  be  used  with  confidence 
where  the  layers  are  artificially  made,  and  where  there  is  no  uncer- 
tainty regarding-  the  uniform  character  of  the  material.  In  most 
natural  channels  there  are  distinct  lines  of  flow,  and  under  con- 
siderable hydrostatic  head  or  pressure  these  lines  of  flow  would 
surely  enlarge.  There  is  a  wide  difference  between  permissible  and 
dangerously  excessive  percolation  through  an  earth  embank- 
ment. The  local  features,  economical  considerations  and  magni- 


58  EARTH  DAMS. 

tude  of  the  risks,  all  bear  upon  this  question  and  must  be  considered 
for  each  particular  case. 

It  is  of  interest  to  compare  the  estimated  cost  of  the  three  de- 
signs proposed  for  the  Bohio  Dam,  based  upon  the  same  unit 
prices,  as  follows : 

French  Engineers'  design     $3,500,000 

Isthmian  Canal  Commissioners'    design 8,000,000 

Mr.  Morison's  design 2,500,000 

No  comments  will  be  made  upon  these  figures,  further  than  to 
remark  that  the  successful  building  of  a  stable  dam,  accomplished 
by  the  use  of  an  excessive  quantity  of  materials  and  at  a  cost  be- 
yond reasonable  requirements,  is  mainly  instructive  as  illustrating 
"how  not  to  do  it."  It  is  creditable  to  execute  substantial  works 
at  a  reasonable  cost,  but  it  reflects  no  credit  upon  any  one  to  con- 
struct them  regardless  of  expense. 

Combined   Rock-fill   and   Earth    Dam. 

Fig.  30  shows  a  section  of  the  Upper  Pecos  River  Dam  near 
Eddy,  N.  M. 

This  dam  is  quite  fully  described  by  Mr.  Jas.  D.  Schuyler,  in  his 
recent  book  on  "Reservoirs  for  Irrigation,  Water-Power  and  Do- 
mestic Water-Supply,"  and  need  not  be  mentioned  in  this  paper, 
further  than  to  call  attention  to  the  combination  of  rock-fill  and 
earth  which  constitutes  its  particular  type  of  construction.  This 
type  of  dam  is  believed  to  be  for  manv  localities  a  very  good  one, 
but  up  to  the  present  time  has  only  been  adopted  for  dams  of 
moderate  height,  under  60  ft. 

The   San  Leaudro   Dam,  California. 

A  section  of  the  San  Leandro  Dam,  near  Oakland,  Cal., 
is  shown  by  Fig.  31.  This  section  was  supplied  by  Mr.  W.  F. 
Boardman,  hydraulic  engineer,  who  superintended  the  construction 
of  the  dam,  from  his  own  private  notes  and  data.  It  differs  mater- 
ially from  sections  heretofore  published,  and  is  5  ft.  higher,  thus 
making  it  rank  as  the  highest  earth  dam  in  the  world  of  which 
we  have  an  authentic  record. 

The  dam  was  commenced  in  1874,  and  brought  up  to  a  height 
of  115  ft.  above  the  bed  of  the  creek  in  1898.  At  the  present  time 
it  is  500  ft.  in  length  on  the  crest  and  28  ft.  wide.  The  original 
width  of  the  ravine  at  the  base  of  the  dam  was  66  ft.  The  present 
width  of  base  from  toe  to  toe  of  slopes  is  1,700  ft.  The  height  of 


DIFFERENT  TYPES  OF  EAR' 


UNr 

DAI 


59 


\ 


60  EARTH  DAMS. 

embankment  above  the  original  surface  is  125  ft.,  with  a  puddle 
trench  extending  30  ft.  below. 

All  that  portion  of  the  dam  within  a  slope  of  2^  on  I  at  the  rear 
and  3  on  i  at  the  face  is  built  of  choice  material,  carefully  selected 
and  put  in  with  great  care.  The  portion  outside  of  the  2\  on  I 
slope  line  at  the  down-stream  side  of  the  dam,  was  sluiced  in  from 
the  adjacent  hills  regardless  of  its  character,  and  is  composed  of 
ordinary  soil  containing  more  or  less  rock. 

This  process  of  sluicing  was  carried  on  during  the  rainy  season, 
when  there  was  an  abundance  of  water,  and  it  was  intended  to  be 
continued  until  the  canyon  below  the  dam  had  been  filled  to  an  av- 
erage slope  of  6.7  on  I  at  the  rear  of  the  dam.  It  was  thought  that 
the  location  was  particularly  favorable  for  this  kind  of  construction, 
the  original  intention  being  to  raise  the  dam  from  time  to  time, 
not  only  to  increase  the  storage  as  the  demand  for  water  increased, 
but  to  meet  the  annual  loss  in  capacity  caused  by  the  silting  up  of 
the  reservoir  basin.  The  latter  has  amounted  to  about  I  ft.  in 
depth  per  annum. 

METHOD  OF  CONSTRUCTION.— Under  the  main  body  of 
the  dam,  the  surface  was  stripped  of  all  sediment,  sand,  gravel  and 
vegetable  matter.  Choice  material,  carefully  selected,  was  then 
brought  by  carts  and  wagons  and  evenly  distributed  over  the  sur- 
face in  layers  about  I  ft.  or  less  in  thickness.  This  was  sprinkled 
with  just  enough  water  to  make  it  pack  well,  not  enough  to  make 
it  like  mud.  During  construction  a  band  of  horses  was  led  by  a 
boy  on  horseback  over  the  entire  work,  to  compact  the  materials 
and  assist  in  making  the  dam  one  homogeneous  mass.  No  rollers 
were  used  on  this  dam. 

The  central  trench  was  cut  30  ft.  below  the  original  bed  of  the 
creek.  In  the  bottom  of  this  trench  three  secondary  trenches,  3 
ft.  wide  by  3  ft.  deep,  were  made  and  filled  with  concrete.  These 
concrete  walls  were  carried  up  2  ft.  above  the  general  floor  of  the 
trench,  to  break  the  continuity  of  its  surface. 

The  original  wasteway,  constructed  at  the  north  end  of  the  dam, 
has  been  practically  abandoned,  having  been  substituted  by  a  tunnel 
of  larger  capacity.  The  original  wasteway  was  excavated  in  the 
bed  rock  of  the  natural  hillside,  and  although  lined  with  masonry, 
is  not  in  the  best  condition.  The  author  considers  its  location  an 
objectionable  feature,  as  menacing  the  safety  of  the  dam,  and  thinks 
it  should  be  permanently  closed. 

A  wasteway  tunnel,  1,487  ft.  in  length,  was  constructed  in  1888, 


DIFFERENT  TYPES  OF  EARTH  DAMS.  6l 

through  a  ridge  extending  north  of  the  dam.  This  has  a  sectional 
area  of  about  10x10  ft.,  lined  with  brick  masonry  throughout,  hav- 
ing a  grade  of  2%%. 

The  criticism  might  be  made  of  the  tunnel  that  it  is  faulty  in 
design  at  the  entry  or  reservoir  end,  where  the  water  must  first 
fall  over  a  high  spillway  wall,  aerating  the  water  before  entering 
the  tunnel  proper.  The  water  even  then  has  not  easy  access  to 
the  tunnel,  and  no  adequate  arrangements  have  been  made  for  ven- 
tilation, so  as  to  insure  the  utilization  of  its  maximum  capacity. 
The  maximum  depth  of  water  in  the  reservoir  is  about  85  ft.,  and 
the  full  capacity  689,000,000  cu.  ft.  of  water.  The  catchment  area 
is  43  square  miles,  and  the  surface  of  the  reservoir  when  full  436 
acres.  The  outlet  pipes  are  placed  in  two  tunnels  at  different  ele- 
vations through  the  ridge  north  of  the  dam.  There  are  no  culverts 
or  pipes  extending  through  the  body  of  the  dam  itself. 

Hydraulic-fill    Dams. 

No  discussion  of  earth  dams  would  be  complete  without  some 
reference  being  made  to  the  novel  type  of  construction  developed 
in  western  America  in  recent  years,  by  which  railroad  embankments 
and  water-tight  dams  are  built  up  by  the  sole  agency  of  water.  The 
water  for  this  purpose  is  usually  delivered  under  high  pressure,  as 
it  is  generally  convenient  to  make  it  first  perform  the  work  of 
loosening  the  earth  and  rock  in  the  borrow  pit,  as  well  as  subse- 
quently to  transport  them  to  the  embankment,  and  there  to  sort  and 
deposit  them  and  finally  part  company  with  them  after  compacting 
them  solidly  in  place,  even  more  firmly  than  if  compressed  by 
heavy  rollers.  Sometimes,  however,  water  is  delivered  to  the  bor- 
row pit  without  pressure,  in  which  event  the  materials  must  be 
loosened  by  the  plow  or  by  pick  and  shovel  by  the  process  called 
ground  sluicing  in  placer  mining  parlance. 

An  abundance  of  water  delivered  by  gravity  under  high  pressure 
is  usually  regarded  as  one  of  the  essential  factors  in  hydraulic-fill 
dam  building,  but  it  is  not  essential  that  there  be  a  large  continu- 
ous flow.  The  Lake  Frances  Dam,  recently  constructed  for  the 
Bay  Counties  Co.,  of  California,  by  J.  D.  Schuyler,  is  75  ft.  high, 
1,340  ft.  long  on  top,  and  contains  280,000  cu.  yds.  The  dam  was 
built  up  by  materials  sluiced  by  water  that  was  forced  by  a  cen- 
trifugal pump  through  a  12-in.  pipe  and  3-in.  nozzle,  against  a  high 
bank,  whence  the  materials  were  torn  and  conveyed  by  the  water 
through  flumes  and  pipes  to  the  dam.  About  6  cu.  ft.  per  sec.  of 


62  EARTH  DAMS. 

water  was  thus  used,  and  at  one  stage  of  the  work  the  supply 
stream  was  reduced  to  less  than  o.i  ft.  per  sec.,  the  water  being 
gathered  in  a  pond  and  pumped  over  and  over  again. 

The  chapter  on  hydraulic-fill  dams  in  Mr.  Schuyler's  book  on 
''Reservoirs  for  Irrigation"  will  be  found  to  contain  matter  on  the 
subject  interesting  to  those  who  desire  to  pursue  it  further,  and 
the  reader  is  again  referred  to  that  work. 

An    Impervious   Diaphragm   in   Earth   Dams. 

As  a  result  of  the  recent  extended  discussion  concerning  the  de- 
sign of  the  New  Croton  Dam  and  the  Jerome  Park  Reservoir  em- 
bankments, the  Engineering  News  of  Feb.  20,  1902,  contained  a 
very  suggestive  editorial  entitled,  "Concerning  the  Design  of  Earth 
Dams  and  Reservoir  Embankments."  The  opinion  is  given  that 
no  type  of  structure  that  man  builds  to  confine  water  can  compare 
in  permanence  with  earth  dams,  after  which  the  following  pertinent 
questions  are  asked : 

1.  How  shall  an  earth  dam  be  made  water-tight? 

2.  What  is  the  office  and  purpose  of  the  masonry  core  wall  ? 

3.  Would  not  a  water-proof  diaphragm  of  some  kind  be  better 
than  a  core  wall  of  either  masonry  or  puddle  ? 

The  article  then  suggests  a  number  of  designs  of  diaphragm  con- 
struction, with  a  special  view  of  obtaining  absolute  water-tight- 
ness, by  use  of  asphaltum,  cement-mortar,  steel  plates,  etc.  Special 
emphasis  was  put  upon  the  principle  of  constructing  a  waterproof 
diaphragm.  The  matter  of  relative  cost  is  advanced  as  an  argu- 
ment in  favor  of  the  diaphragm  principle  as  against  the  usual  ortho- 
dox method.  The  saving  in  cost  is  to  be  accomplished  by  the  use 
of  inferior  materials  and  less  care  in  the  handling  of  them,  or  by 
both.  It  is  suggested  that  almost  any  kind  of  material  available, 
rock,  sand  or  gravel,  will  answer  every  purpose  where  good  earth 
is  not  to  be  found.  Further,  that  this  material  may  be  dumped  from 
the  carts,  cars  or  cableways,  or  be  placed  by  Hie  hydraulic-fill 
method. 

The  writer  believes  the  diaphragm  method  of  construction  may 
have  some  merits,  but  that  it  is  attended  by  the  very  great  risk  of 
neglecting  principles  most  vitally  important  to  the  successful  con- 
struction of  high  earth  dams,  which  will  now  be  formulated  and 
advanced,  as  follows : 


CHAPTER  VI. 
Conclusions. 

The  writer  in  concluding  this  study  wishes  to  emphasize  certain 
principles  and  apparently  minor  details  of  construction,  which  from 
observation  and  personal  experience,  seem  to  him  of  vital  import- 
ance. 

He  believes  firmly  in  the  truth  contained  in  the  following  re- 
marks by  Mr.  Desmond  FitzGerald,  of  Boston,  germane  to  this 
subject: 

An  engineer  must  be  guided  by  local  conditions  and  the  resources  at  his 
command  in  building  reservoir  embankments.  His  design  must  be  largely 
affected  by  the  nature  of  the  materials.  There  are  certain  general  principles, 
however,  which  must  be  observed  and  which  will  be  applied  by  an  engineer 
of  skill,  judgment  and  experience  to  whatever  design  he  may  adopt  It  is 
in  the  application  of  these  principles  that  the  services  of  the  professional  man 
becomes  valuable,  and  it  is  from  a  lack  of  them,  that  there  have  been  so 
many  failures. 

The  details  and  principles  of  construction,  relating  to  high  earth 
dams,  may  be  summarized  or  stated  in  order  of  their  application, 
as  follows: 

(i)  Select  a  firm,  dry,  impermeable  foundation,  or  make  it  so  by 
•excavation  and  drainage.  All  alluvial  soil  containing  organic  mat- 
ter and  all  porous  materials  should  be  excavated  and  removed 
from  the  dam  site  when  practicable;  that  is,  where  the  depth  to  a 
suitable  impermeable  foundation  is  not  prohibitive  by  reason  of  ex- 
cessive cost. 

Wherever  springs  of  water  appear,  they  must  be  carried  outside 
the  lines  of  the  embankment  by  means  of  bed  rock  drains,  or  a  sys- 
tem of  pipes  so  laid  and  embedded  as  to  be  permanent  and  effective. 

The  drainage  system  must  be  so  designed  as  to  prevent  the  in- 
filtration of  water  upward  and  into  the  lower  half  of  the  embank- 
ment, and  at  the  same  time  insure  free  and  speedy  outlet  for  any 
seepage  water  passing  the  upper  half.  All  drains  should  be  placed 
upon  bed  rock  or  in  the  natural  formation  selected  for  the  foun- 
dation of  the  superstructure.  They  should  be  constructed  in  such 
a  manner  as  to  prevent  the  flow  of  water  outside  the  channel  pro- 
vided for  it,  and  also  prevent  any  enlargement  of  the  channel  itself. 


64  EARTH  DAMS. 

To  this  end,  cement,  mortar,  broken  stone,  and  good  gravel  puddle 
are  the  materials  best  suited  for  this  purpose. 

(2)  Unite  the  body  of  the  embankment  to  the  natural  foundation 
by  means  of  an  impervious  material,  durable  and  yet  sufficiently 
elastic  to  bond  the  two  together.     When  the  depth  to  a  suitable 
foundation  is  great,  a  central  trench  excavated  with  sloping  sides, 
extending  to  bed  rock  or  other  impervious  formation,  refilled  with 
good  puddling  material,  properly  compacted,  will  suffice. 

When  clayey  earth  is  scarce  and  expensive  to  obtain,  a  small 
amount  of  clay  puddle  confined  between  walls  of  brick,  stone  or 
concrete  masonry,  and  extending  well  into  the  body  of  the  embank- 
ment and  so  built  as  to  avoid  settlement,  will  prevent  excessive 
seepage.  This  form  of  construction  is  not  to  be  carried  much 
above  the  original  surface  of  the  ground. 

(3)  The  continuity  of  surfaces  should  always  be  broken,  at  the 
same  time  avoiding  the  formation  of  cavities  and  lines  of  cleavage. 
No  excavation  to  be  refilled  should  have  vertical  sides,  and  long 
continuous    horizontal   planes    should    be   intercepted   by   wedge- 
shaped  offsets,  enabling  the  dovetailing  of  materials  together. 

All  loose  and  seamy  rock  or  other  porous  material  should  be 
removed,  and  where  the  refill  is  not  the  best  for  the  purpose,  mix 
the  good  and  bad  ingredients  thoroughly,  after  which  deposit  in 
very  thin  layers. 

(4)  Make  the  dimensions  and  profile  of  dam  with  a  factor  of 
safety  against  sliding  of  not  less  than  ten.     The  preliminary  cal- 
culations for  designing  such  a  profile  have  been  given  on  p.  42. 

(5)  Aim  at  as  nearly  a  homogeneous  mass  in  the  body  of  the  em- 
bankment as  possible,  thus  avoiding  unequal  settlement  and  de- 
formation.    This  manner  of  manipulating  materials  will  eliminate 
many  uncertain  or  unknown  factors,  but  it  means  rigid  inspection 
of  the  work  and  intelligent  segregation  of  materials,  no  matter  what 
method  of  transporting  them  may  be  adopted.    The  smaller  the  unit 
loads  may  be,  the  more  easily  a  homogeneous  distribution  of  ma- 
terials will  be  obtained. 

(6)  Select  earthy  materials  in  preference  to  organic  soils,  with  a 
view  of  such  combination  or  proportion  of  different  materials  as  will 
readily    consolidate.      Consolidation   is   the   most   important    process 
connected  with  the  building  of  an  earth  dam.     The  judicious  use  of 
soil  containing  a  small  percentage  of  organic  matter  may  be  per- 
mitted, however,  when  there  is  a  lack  of  clayey  material  for  mixing 
with  sandy  and  porous  earth  materials.    Such  a  mixture,  properly 


CONCLUSIONS.  65 

distributed  and  wetted,  will  consolidate  well  under  heavy  pressure 
and  prove  quite  satisfactory. 

(7)  Consolidation  being  the  most  important  process  and  the  only 
safeguard  against  permeability  and  instability  of  form,  use  only  the 
amount  of  water  necessary  to  attain  this.     Too  much  or  too  little 
nre  equally  bad  and  to  be  avoided.     It  is  believed  that  only  by  ex- 
periment and  experience  is  it  possible  to  determine  just  the  proper 
quantity  of  water  to  use  with  the  different  classes  of  materials  and 
their  varying  conditions.    In  rolling  and  consolidating  the  bank,  all 
portions  that  have  a  tendency  to  quake  must  be  removed  at  once 
and  replaced  with  material  that  will  consolidate ;  it  must  not  be  cov- 
ered up,  no  matter  how  small  the  area. 

(8)  In  an  artificial  embankment  for  impounding  water  it  is  im- 
practicable to  place  reliance  upon  time  for  consolidation ;  it  must  be 
effected  by  mechanical  means.     Again  we  repeat,  that  consolida- 
tion is  the  most  vitally  important  operation  connected  with  the 
building  of  an  earth  dam.    When  this  is  satisfactorily  attained  it  is 
proof  that  the  materials  are  suitable  and  that  the  other  necessary 
details  have  been  in  a  large  measure  complied  with.     Light  rollers 
are   worse   than   useless,   being  a   positive   harm,   resulting   in   a 
smoothing  or  ''ironing  process,"  deceptive  in  appearance  and  detri- 
mental in  many  ways. 

The  matter  of  supreme  importance  in  the  construction  of  earth 
dams  is  that  the  greatest  consolidation  possible  be  specified  and 
effected.  To  this  end  it  is  necessary  that  heavy  rollers  be  em- 
ployed, and  that  such  materials  be  selected  as  respond  best  to  the 
treatment.  There  are  certain  kinds  of  earth  materials  which  no 
amount  of  wetting  and  rolling  will  compact.  These  must  be  re- 
jected as  Unfit  for  use  in  any  portion  of  an  earth  dam.  Let  the  de- 
sign of  the  structure  be  ever  so  true  to  correct  engineering  prin- 
ciples, it  is  still  necesssary  to  give  untiring  attention  to  the  work  of 
consolidation.  It  is  therefore  according  to  the  design  of  a  thor- 
oughly compacted  homogeneous  mass,  rather  than  to  the  suggested 
diaphragm  type,  to  which  modern  practice  should  conform.  This  is 
in  harmony  with  Nature's  own  methods,  and  in  conformity  to  cor- 
rect principles. 

(9)  Avoid  placing  pipes  or  culverts  through  any  portion  of  the 
embankment.     The  writer  considers  it  bad  practice  ever  to  place 
the  outlet  pipes  through  a  high  earth  dam,  and  fails  to  see  any  nec- 
essity for  so  doing. 

(10)  The  surface  of  the  dam,  both  front  and  rear,  must  be  suit- 


66  EARTH  DAMS. 

ably  protected  against  the  deteriorating  effects  of  the  elements. 
This  may  include  pitching  the  up-stream  face,  the  riprap  work 
at  the  toe  of  the  inner  slope,  the  roadway  and  covering  of  the 
crown,  the  sodding  or  other  protection  of  the  rear  slope,  and  the 
construction  of  surface  drains  for  the  berms. 

(n)  Ample  provision  for  automatic  wasteways  should  be  made 
for  every  dam,  so  that  the  embankment  can  never  under  any  cir- 
cumstances be  over-topped  by  the  impounded  water.  Earthquakes 
and  seismic  disturbances  will  produce  no  disastrous  effects  upon 
an  earth  dam.  Its  elasticity  will  resist  the  shock  of  water  lashing 
backwards  and  forwards  in  the  reservoir. 

(12)  Finally,  provide  for  intelligent  and  honest  supervision  dur- 
ing construction,  and  insist  upon  proper  care  and  maintenance 
ever  afterwards. 


APPENDIX   I. 
High  Earth  Dams. 


Name  of  Dam  or 
Reservoir. 


— Embankment — > 


Location. 


Max. 

height, 

ft. 


S 


San  Leandro California 125 

7  Tabeaud California 123 

Druid  Hill Maryland 119 

Dodder Ireland 115 

Titicus  Dam New  York no 

Mudduk  Tank India 108 

Cummum  Tank. . .  India 102 

Dale    Dike England 102 

Marengo Algeria 101 

Torside England 100 

7  Yarrow England 100 

Honey  Lake California 96 

Pilarcitos California 95 

San  Andres California 95 

Temescal California 95 

Waghad India 95 

Bradfield England 95 

Oued  Meurad Algeria 95 

St.  Andrews Ireland 93 

Edgelaw Scotland 93 

Woodhead England 90 

Tordoff Scotland 85 

Naggar India 84 

Vahar India 84 

Rosebery Scotland 84 

Atlanta Georgia 82 

Roddlesworth England 80 

Gladhouse Scotland 79 

Rake England 78 

Silsden England 78 

Glencourse Scotland 77 

Leeshaw England 77 

Wayoh England    76 

Ekruk  Tank India 76 

Nehr India 74 

Middle  Branch . .  .  New  York 73 

Leeming Ireland 73 

South  Fork Penna 72 

Anasagur India 70 

Pangran India 68 

Harlaw Scotland 67 

Lough  Vartry Ireland 66 

La  Mesa California  ....  66 

Amsterdam New  York 65 

Mukti India 65 

Snake  River California 64 

Stubken Ireland 63 

Den  of  Ogil Scotland 60 

Loganlea Scotland 59 

Ashti India 58 

Cedar  Grove New    Jersey...  55 


Top 

width, 

ft. 

28 

20 

60 

22 


Slopes > 

Water.  Rear. 


Avail- 
able 
depths, 
ft. 


12 


24 
2O 
25 
25 
12 

6 

12 
25 


24 
40 

16 

12 


22 

20 

8 

TO 
2O 
2O 

8 
28 

20 

10 
12 

24 

IO 

6 
18 


3  on  i 

4  on  i 

2)4  on 
2  on 

[     70 
[     82 

3)^  on  i 
2  on  i 
3  on  i 

3  on 

2)4  on 
2)4  on 

I 
[ 

3  on  i 

i  on 

2)4  on 

90 



.  .  . 

84 

3  on  i 

2  on 

3  on  i 
2^  on  i 
3/5  on  i 

2  on 

2)4  on 
3  on 

•• 

3  on  i 
3  on  i 
2)4  on  i 

2  on 
2  on 

2)4  on 

81 

3  on  i 

2)4  on  i 

72 

3  on  i 

2)4  on  i 

3  on  i 

2)4  on  i 

•• 

3  °n 
3  on 
3  on 

3  °n 
"?  on 

2)4  on  i 
2)4  on  i 
2  on  i 
2  on  i 

68 
68 

3  °n 
3  on 

2)4  on  i 
2  on  i 

65 

3  on  i 
2  on  i 
4  on  i 

2  on  i 

1)4  on  i 

50 
42 

64 

3  on  i 
ijioni 

2)4  on  i 
i)4  on  i 

60 
60 

3  on  i 
2  on  I 
3  on  i 

2  on  i 
1)4  on  I 
2  on  i 

CO 

3  on  i 
3  on  i 
3  on  i 

2)4  on  i 
2  on  i 
2  on  i 

55 
42 

APPENDIX.— II. 

Works  of  Reference. 
Author.  Title.  Date. 

Baker,  Benj The  Actual  Lateral  Pressure  of  Earthwork. .   1881 

Baker,  Ira  O Treatise  on  Masonry  Construction 1899 

Bell,  Thos.  J History  of  the  Water  Supply  of  the  World .   1882 

Beloe,  Chas.  H Beloe  on  Reservoirs 1872 

Bowie,  Aug.  J.,  Jr A  Practical  Treatise  on  Hydraulic  Mining.  .   1898 

Brant,  Wm.  J Scientific  Examination  of  Soils 1892 

Brightmore,  A.  M The  Principles  of  Water-Works  Engineering.  1893 

Buckley,  Robt.  B Irrigation  Works  in  India  and  Egypt 1893 

Cain,   Wm Retaining  Walls   1888 

Chittenden,  H.  M Report  and  Examination  of  Reservoir  Sites 

in  Wyoming  and  Colorado 1898 

Courtney,   C.    F Masonry  Dams 1897 

Fanning,  J.  T Water-Supply  Engineering 1889 

Flynn,  P.  J Irrigation     Canals      and      Other     Irrigation 

Works 1892 

Frizell,  Jos.  P Water  Power 1891 

Gordon,  H.  A Mining  and  Mining  Engineering 1894 

Gould,  E.  S The  Elements  of  Water-Supply  Engineering.  1899 

Hall,  Wm.  Ham Irrigation  in  California 1888 

Hazen,  Allen The  Filtration  of  Public  Water  Supplies 1895 

Howe,  M.  A Retaining  Walls  for  Earth 1891 

Hughes,    Saml Treatise   on  Water- Works 1856 

Jackson,  L.  TX  A Statistics  of  Hydraulic  Works 1885 

Kirkwood,  J.  P Filtration  of  River  Waters 1869 

Merriman,  M Treatise  on  Hydraulics,  Masonry  Dams  and 

Retaining  Walls 1892 

Newell,  F.  H Irrigation  in  the  United  States 1902 

Newman,  John Earthwork  Slips  and  Subsidences  Upon  Pub- 
lic Works    1890 

Potter,  Thomas Concrete   1894 

Schuyler,  J.  D Reservoirs  for  Irrigation,  Water  Power  and 

Domestic   Water    Supply 1901 

Slagg,   Chas Water    Engineering    1888 

Stearns,  F.  P Metropolitan  Water-Works  Reports 1897 

Stockbridge,  H.  E Rocks  and  Soils 1888 

Trautwine,  J.  C Earthwork;  and  Engineer's  Pocket-Book 1890 

Turner,  J.   H.   T The  Principles  of  Water- Works  Engineering.  1893 

Wilson,  J.  M Manual    of   Irrigation    Engineering 1893 

Annual  Reports. 

Massachusetts  State  Board  of  Health. 

Geological  Survey  of  New  Jersey. 

Metropolitan  Water- Works,   Boston  and  vicinity. 

U.  S.  Geological  Survey. 

Transactions  American  Society  of  Civil  Engineers. 

Vols.  3,  15,  24,  32,  34  and  35. 
Proceedings  of  the  Institution  of  Civil  Engineers. 

Vols.  59,  62,  65,  66,  71,  73,  74,  76,  80,  115  and  132. 
Engineering  News.     Vols.   19  to  46. 
Engineering  Record.     Vols.   23  to  46. 
Journal  of  the  Association  Engineering  Societies.     Vol.  13. 


INDEX. 

Page 

Analyses,  soil,  Tabeaud  Dam 25 

Analyses   of   soils 14 

Tabeaud   Dam 25 

Borings,  wash  drill,  Wachusett  Dam 48 

Catchment  area 3 

Clay   for  puddle 15 

Contractors'  outfit,  Tabeaud  Dam 31 

Core  wall,  impervious  diaphragm  as  substitute  for 62 

necessity   for 44 

(See  puddle.) 

Dam,  Ashti,  India 35 

Bog   Brook 41 

Bohio,  Panama  Canal 54 

Croton  Valley,  slope  of  saturation  in , 40 

different  types  of  earth 33 

Druid   Lake,   Baltimore 52 

high  earth,  statistical  table  of 67 

hydraulic  fill 61 

hydraulic  fill,  San  Leandro 60 

ideal  profile  of 42 

Isthmian  Canal  Commission 54 

Lake  Frances  hydraulic  fill 61 

New    Croton 39 

graphical  study  of  original  earth  portion  of 43 

New  England,  typical  section  of 40 

new  types  of 54 

^             North  Dike,  Wachusett  Reservoir 48 

rock-fill  and  earth  combined,  upper  Pecos  River 58 

safe  height  of 39 

San    Leandro 58 

site   location 7 

Tabeaud 1.3,  17 

Titicus. 41 

Upper  Pecos  River  rock-fill  and  earth 58 

with  puddle  core  wall  or  face 33 

Yarrow,  Liverpool  water- works 9,  33 

Diaphragms  impervious  for  earth  dams 62,  65 

^.J     Dike,  north  of  Wachusett  Reservoir  (see  Dam;  also  reser- 
voir). 

Drainage  and  slips  of  earthwork 45 

of  dam  sites 63 


70  INDEX. 

Page 

Drains,  bed  rock,  Tabeaud  Dam 19 

Earthwork  slips  and  drainage 45 

Embankment,  Ashti,  India 35 

Embankments,  Jerome  Park  Reservoir 45,  46 

Factor  of  safety  for  dams 64 

Filtration,   experiments  on  nitration  through  soils  at  Wa- 

chusett  Reservoir 50 

formula,  Hazen's .__._.  56 

Foundations 9,  63 

Gravel  for  puddle 15 

Infiltration  and  percolation 38 

Isthmian  Canal  Commission,  designs  of  dams  for 54 

Outlet  pipes  and  tunnels 6 

Percolation 38,  57 

Profile,  ideal  for  dams 42 

Puddle    14 

core  wall,  Ashti  Dam 35 

or   face 33 

trench   37 

wall,  Druid  Lake  Dam 53 

for  Yarrow  Dam 34 

vs.  puddle  face 37 

Reservoir  basin. 37 

outlets 6 

Wachusett  48 

Rollers  for  dams 30,  65 

Sands  and  gravels,  flow  of  water  through. 52 

(Also  see  percolation.) 

Slips  and  drainage  of  earthwork 45 

Soil  analyses,  Tabeaud  Dam 25 

analysis     14 

Soils,    experiments    on    filtration    through    at    Wachusett 

Reservoir 50 

outline  study  of 12 

permanence  of 51 

selection  of,  for  dams 64 

studies,  Wachusett  Reservoir 50 

Spillway  or  wasteway 8 

^          Tabeaud  Dam 31 

Subsidences,   earthwork 45 

Test  pits 5,  8,  9 

^      Tunnel,  outlet,  Tabeaud  Dam 30 

Tunnels  as  outlets  to  reservoirs 6 

Wasteway   or   spillway 8,  66 

Tabeaud   Dam  •  •  •     i»trtir  ii,,    • 31 


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